its definitly related to the last transaction from nicehash in combination with v0.21.0, the problem just start after that transaction.
Transaction ID:
v0.20.1 worked just fine for me again, but I reinstalled v0.21.0 to verify the problem.
Clean dbug.log and start with -reindex and -rescan.
After running for a couple of hours I went for dinner, synching sometime in 2017, when I came back Bitcon Core was shutdown.
Restart 2 times with same resault, the programm crashes without any error messege.

look at the debug.log, especially the entries in 800 and 1016 when programm crashes:

its the transaction from nicehash....

Now running v0.20.1 again, debug.log so far below, look at 206, its still synching without problem: