That will do, but take note that the said command will just generate 50 more addresses instead of increasing the wallet's gap limit.
After the last address was used, your wallet will only generate a number of addresses depending on the gap limit.

@NectarM To set the gap limit, use this command instead:
Change '50' depending on your preference.

Did you set a "passphrase" during your first "new device setup"?
If so, you have to enter the same passphrase when you reset your ledger using the 24-word mnemonic.
A different passphrase will create an entirely different wallet.

Also, where is the source of the steps that you've followed?
Because there are couple of phishing emails/articles lately that uses social engineering to get the seed phrase of hardware wallet users.

That transaction from 2018 was saved in your wallet.dat but probably have been offline after the input was spent in 2019
and somehow failed to fetch the latest transaction that spent the "missing (spent) input" during your last sync.

Running Bitcoin core with -rescan (don't if you're using a pruned node) will 'fix' the issue but that won't recover the already spent inputs.
It will just show your real balance which may be 0BTC if you do not have other addresses with balance.
Does your transaction has more than one inputs?
Because if at least one of them is invalid, it will result with the same error, in that case -rescan will also eliminate the missing input(s).

Do you recognize this transaction from 2019, because it spent your balance from 2018?
313cb0b28d23f6e8afdb9f93bf047d41360745881ecdd9e387e10f067cd1bc8a

You still haven't replied to your other thread.
But based from this, you likely have used missing or already spent inputs for that transaction.
It's best if you can manually send it to your own mempool to see what error message you'll get.

What you need to do is to answer these questions:
Where did your balance came from?
What error did you get when you tried to send it to your mempool using these instructions:

"Right-click menu" is the menu when you right-clicked the transaction in the 'Transactions' tab.

"sendtoaddress" will work is that case.
Given the example, the "coin selection algorithm" will automatically select the best input(s) from those available 4.
I'd say it will pick Input B + Input C if you want to send 0.006 BTC using sendtoaddress.

However, you'll be needing to consolidate in real-world case since there will be a lot of much smaller UTXOs.
For that, you will definitely have to create the transaction, sign and broadcast manually if you're using Bitcoin Core's RPC.
Alternatively, the GUI have a "coin-control" feature that can be toggled on.

BTW, since you've mentioned "Bitcore", there may be more alternatives using its wallet service; but I can't help you with that.

Just re-read what HCP have posted,
the instruction is to get the "private keys" of your addresses with balance then import it to Electrum.
There's also a link on how to get the keys from Armory.

If you do not have Armory installed, just install Armory and restore your wallet first.
Then you can extract the private keys even if Armory is offline.

(lol) actually there were two "ETHpill" posts below scryptr's post before the newly posted one.

You can ask for assistance in meta (board link) to get the attention of the admin.
And members there may brainstorm some possible solutions to this issue.

Is it about blockchain.com?
Yes? Their fee rate is based on their own api, you can check it in action here: https://api.blockchain.info/mempool/fees
Those are the same result that the "send" window will show you for 'regular' and 'priority' fee rates.

And the priority fee (even regular) is indeed an overestimation.

I'd suggest you put a short/complete summary or description in the OP  
Because with only a single link, moderators will likely delete it in a few hours.

Yes along with their other features.

This depends on what's being explained by the writer.
If talking about bitcoin addresses and wallets, then it points to a wallet since it's generally a "human-readable encoding" of the public key hash, and the public key is contained in your wallet.
If it's about the blockchain not your wallet, then there're no addresses involved but only the scripts they represent.

If just the icons, then it's doable with no coding knowledge (but minor editing skills and/or tools are required).
All you have to do is to edit/replace some icons here: https://github.com/spesmilo/electrum/tree/master/electrum/gui/icons
Example:


The icons' names should be the same and it should be in "8-bit png" "sRGB web format" in order not to get error messages.
(could be different but it works without errors at my end)
Then run Electrum from source or compile it.

Check-out my (ugly) DarkMode&Red Electrum - running from source (Dark Mode - on):

I want the connection icon red so, I've allocated a small green circle for the actual connection status.

I'm still waiting for his reply after trying to broadcast the transaction, but he replied with a replay of the OP.
Because it might return an error msg that could be the reason why it's "not in memory pool" if there was an issue with the txn.

@Chandu141 at least say if you have already tried the suggestions and post the results.

Means that the transaction isn't even in your own mempool.

You can use the console command sendrawtransaction to broadcast it ('Window->Console' to open console).
Just get that particular txn's "RAW transaction" using the right click menu and paste that after the command.
eg:

Do you happen to have an entry like walletbroadcast=0 on your bitcoin.conf?
If so, remove it or set it to "1".

AFAIR, I've read somewhere that it works in mainnet.
It's just that the difficulty is too high that it'll surely fail after the default 'maxtries' (1000000 iterations).

I'll try to find the post (from a Bitcoin Core developer) and update this later.

-edit-

Found it: /index.php?topic=5227792.msg53894613#msg53894613
Thanks google search.

I too have sent an email to their support since my yesterday post's timestamp.
But I never received a reply.

Maybe it was redirected directly to their technical team.

The current average fee rate is quite low, now even 3sat/vB is enough for a fast confirmation.
You might want to send while the average mempool size is low.

The verdict is fine since there's no way to produce a reproducible build for the android version (latest post of the issue).

They also got a point when they mentioned that the google play version is different from the development build that they successfully compiled
since Electrum Devs are working on the "master branch" rather than a development branch, the source at that point has a few/lot of commits ahead from the google play version.

---

Okay, this is the last of Electrum-specific discussion for me here.

This approximation of the common inputs looks close enough: https://bitcoin.stackexchange.com/a/87276
That's if you don't need the actual numbers, otherwise getting SegWit inputs' virtual size will be complicated (example).

Aside from the post above, there's another inconsistency on that site:

It was published on 2019 Dec 11:
But it said that the latest version is v4.0.4.0:
FYI, electrum v4.0.4 (not v4.0.4.0) was only released on 2020-October-15.

I wouldn't trust that page if I were you since they can't differentiate fake electrum and the original.
Update: I have read the whole article and it looks like that the version written in the page was updated somehow but other links like readme.md aren't.
The date and version are still misleading.

Coinbox seems to be using a different "derivation path" than Electrum's default.
I've tried various paths but nothing restored the first '3' nor 'bc1' address of coinbox.

I'll try some other variations and update you later if I've found the correct one.
For now, if it has balance, try using "Detect Existing Accounts" in the 'Script type and Derivation path' selection window of Electrum during wallet restore session.

There's a simpler way to send transactions without going through the "advanced preview".
You just have to disable "Advanced preview" in the settings: "Tools->Preferences->'Transactions' tab".

That way, it'll be signed and broadcast automatically after you click "send" under the "confirm transaction" dialogue box when you clicked "send" in the send tab.
But if you want to open the advanced preview, you can click "Advanced" in the same dialogue box.