After turning off backup metadata verification (from
WT-8561 analysis) which was causing recovery to not run, I started running a general randomized mirror configuration overnight.
It hit an assertion:
What the mirror checking does is walk the standard keys in all the mirror tables. All standard keys should be the same. Then if the keys are the same, it checks the values, which are all updated to the same values in a single transaction.
In this case, the keys are not the same. The base table, T00001 appears to be missing one since the key numbers are added sequentially: