It is crazy. I was just about to send 0.2btc and i have to pay more than 0.006 fee! This is outrageous! Almost 300k unconfirmed transactions and it's not getting any better

Hey, dont worry about this, it happened to me the same using my hardware wallet a few days ago, it was a transaction of about $2000 and i was very scared just like you are right now.

I sent it, and then it disapeared from the blockchain.

It was more than 13 without any confirmation (because it was displayed on my wallet), and it didn't appeared on blockchain.info, not even on blockcypher or any of those block explorers.

A few hours after when i got the first confirmation it suddenly appeared on the other wallet, and it was on the blockchain too.

It is just matter of time until it gets the first confirmation, with the actual congestion, it might take DAYS or WEEKS.

If you have a look at https://blockchain.info/address/1DL6CQ5LCFa517cAiHJ7Z9KEpRL1mEjWpP you can see your final balance after the 9th transaction is roughly 0,5 BTC

The 9th (last) transaction is still unconfirmed, so if that was the transaction you have mentioned in the OP (the amount is the same, 3,05 BTC), then it's still pending and waiting for confirmation. You have sent it with 227 sat/B fee, which is way too little nowdays... (but really much anyway).
You can check also the average tx fee at fork.lol, it's now above 700 sat/B which is ATH too...
You can try to accelerate your transaction in several ways, there's ViaBTC and in the services section you can find other options.
I can just imagine that coinbase also sees the transaction pending, so they haven't received your coins but they can see the unconfirmed transaction and they are still waiting for the confirmations.

no, the coins reappeared in mycelium when i cancelled the transaction and refreshed my wallet, my unconfirmed transaction was visible for hours too, it doesnt mean anything unless its confirmed,neither does an email from coinbase or a letter from the pope

you need to figure out how to cancel the transaction in bitcoin core for android or export your private keys to a wallet that allows you to do such a thing. forget about contacting coinbase because they don't have your coins.

if a transaction isnt showing up on block explorer it doesn't exist, there's nothing coinbase or whoever was meant to be receiving can do about it

recently had a transaction from mycelium to trezor showing up in trezor as unconfirmed for ages, once i cancelled it on mycelium the pending trezor balance disappeared, this transaction also appeared temporarily on the block explorer then went away

Now many online unconfirmed transactions,I think because of this. I have already two days do not come and there is no transaction no confirmation

if the transaction isn't showing up on block explorer it cant have anything to do with coinbase, try right clicking the transaction in core then hit "abandon transaction" and see if the coins don't reappear in your wallet

Well, theoretically it is possible to withdraw a transaction from the pool, but it has been seen and it can be always replayed, so it is not recommended. I wouldn't do that myself, anyway, I understand it too little.

Coinbase on the other hand is a different story, they might have done it purposefully because they understand the behaviour very well, or maybe it was just an incident in their system.

So I would go ahead with a formal complaint if I were you and do it ASAP. I bet eventually the money will be found

I love how "coins are decentralized" always shoots you in the foot.

You don't have an input equal to X+fees so the wallet creates one from some other input say 5X+fees subtracts the amount X being sent to some address and then send the change 4X to another address within your wallet.

Don't use any traditional wallets myself, but my guess is that those are change addresses. They do not show up but they are in your wallet, when you'll try to spend them you will be able to.