Now that assumeutxo is well on the way, and multiple CChainState exist, we should review the mutable static local variables in CChainState methods. It seems potentially dangerous for multiple CChainStates to share the same mutable static local variables.

In CChainState::FlushStateToDisk:

In CChainState::LoadExternalBlockFile (this is fixed by #20331):

ping @jamesob

Now that I think about it... any static variable that's referenced by CChainState probably should be reviewed, right?