Yes I did one (1) BTC transaction from my electrum Wallet to my own Coinbase exchange/Vault address. My receiving address on Coinbase is: 3BVy8iSzyFGYSzqngk1tdhYiLCMuucRFZB
This address does not appear in either of those transactions and there is no transaction history for it:
so you have NOT sent any funds to it.
In electrum I made sure I had the correct address as recipient and under Send Tab - it s hows that transaction (1) with date, Transfer,. amount and status In there I can see that the BTC address of the recipient is the correct address I put in (mine), status is showing "unpaid".
"Unpaid" tells me that what you've done is setup a transaction but then clicked "Save" instead of "Pay...".
Effectively, you entered the address, the amount and then didn't actually sign or broadcast the transaction. I am assuming your "Send" tab looks something like this:
If you right click that "Invoice" item and then select "Details" it will probably show something like this:
except with your 3BVy8iSzyFGYSzqngk1tdhYiLCMuucRFZB address showing.
In the History transaction tab I have suddenly 2 entries (1 for 0.000178 and one for 0.231932) - equaling the total amount I was sending 0.23211.
I did not cancel anything, no bump fees. I hit transfer, it created the invoice piece that is showing unpaid,. but the money is gone. And do I know who or what the 2 addressees where that the tokens were sent to: absolutely not. I only out in my address.
Unknown addresses that I have no clue where they came from but are showing in the transaction details and highlighted in yellow as "Wallet change":
bc1qj2ay5m3l45klwappmqu9zw7ddlqlydr5mqeppw
bc1qfk6ky2r2ww7tkn4ymt59t4lq85rerthfemz3xr.
I have no explanation for where these other addresses/transactions came from... there is certainly something weird happening. Either your seed/wallet has been compromised and a 3rd party has restored your wallet and moved the funds, or the copy of Electrum you are using is "bad"™.
Given you stated you checked digital signatures etc, then it would appear your seed/wallet has been compromised in some other way.