The whole idea of leaving the datadir on the NAS was to not need to re-download the entire blockchain WHEN something like this happened. I'm pretty disappointed with the Bitcoin Core program.
If you can't roll back your backup, I don't think Bitcoin Core is at fault.
I've had the occasional redownload of the entire blockchain, which is annoying but completed in a day (on my old laptop).
For lack of alternatives, I will probably have to delete the blocks and start all over. Given my experience, I probably won't use the NAS next time
Try to at least put the
chainstate directory on a local SSD, that makes a huge difference on performance.
and eventually, I will try to navigate away from needing Bitcoin Core because it creates problems for me.
I've used different wallets, depending on what I need. Bitcoin Core is for instance great for privacy, but Electrum is much easier to use with an online watch-only wallet and offline wallet for signing.