Rewrote more clearly below.

I don't know how much of this is relevant, sorry.

I sent all coins from one computer to my main one leaving an empty, but used, wallet. I deleted it. I sent .01 to the new wallet. While the tx was still unconfirmed I backed it up and deleted it. Later I swapped it back in and it still says unconfirmed even though the computer that sent has it confirmed now. I used -rescan, it was an old version (3.15) and now I've got 3.21 and still the same. What happened? Do I need to reload all blocks?

I send all coins from wallet A to wallet B. Delete wallet A. Send .01 from wallet B to wallet C which appeared after wallet A was deleted. Before the tx gets confirmed I backup wallet C and delete it. Later I restore wallet C and the tx is still showing unconfirmed, but it is confirmed according to wallet B and blockexplorer.

I tried rescan, I upgraded from 3.15 to 3.21 and tried rescan again. Nothing. I assume deleting the blockchain and redownloading will work, but what's going on? Should I try something else first?

I have made another tx from B to C and it worked.