If you have the HD seed you should be able to recover the wallet by importing it into supported wallets like Electrum but how did you get the HD seed? Since BitcoinQT/Bitcoin core doesn't generate a seed I'm sure it was not from this wallet.
It's the "
HDSeed" of Bitcoin Core (
non-descriptor) wallet files which is exported in WIF format.
It cannot be imported to Electrum even if it's converted to (
xprv) master private key since it doesn't support hardened address derivation path.
Another one with bitcoin-qt encryption
then I reverted to the original,
Your old HDSeed's keystore was flushed with the wallet encryption, then if you generated new addresses to receive those missing transactions, then that's the issue.
Encrypting the wallet file will trigger it to set a new HDSeed; so after reverting to the original, you essentially removed the new HDSeed where the new addresses are derived from.
In this case, the solution is to find a backup of that encrypted wallet file.