Sure seems like there is something else going on here.
Several colleagues with your same preamp with few issues like this.
Sourced several tested and matched pairs 12AU7 and 12AT7 tubes from many of the same providers you have with minimal issues.
A good tech?
Might be worth taking the amplifier and preamp to a good tech, checking with clean power and to confirm if any damaged occurred to the amp or preamp during all of these tests. Or, to at least find the real root cause. Could save you a lot of time and $ too. Best of Luck.