I just accidentally quit the mainnet wallet while it was mining RandomX and (on two restarts) I got (this both times)

$ ./veil-qt
Assertion failed: (!setBlockIndexCandidates.empty()), function PruneBlockIndexCandidates, file validation.cpp, line 3467.
Abort trap: 6

It's been a while since I've had that. I thought something else had the foreground when I quit. (I'll check where that problem belongs. Thought it had been fixed.) (Note: snapshot, and reindex-chainstate did not fix this. Wallet.dat was corrupted.)
The repeated error after the chainstate reindex attempt was

$ ./veil-qt -reindex-chainstate
Assertion failed: (false), function forced_return, file /home/runner/work/veil/veil/source/depends/x86_64-apple-darwin14/share/../include/boost/variant/detail/forced_return.hpp, line 47.

The related past issues were #405 and #371. 405 had been closed, presumed fixed in release v1.0.3.0, and those instances had been fixed with -reindex-chainstate. The 371 version of this problem had happened on Linux, had failed to be fixed with a snapshot, and -reindex-chainstate had also failed. The only solution had been to abandon the wallet.dat.

Originally posted by @seanPhill in #921 (comment)