We were previously informed that UPGRADE_PARAMIKO=True caused occasional web page crashes on Rocky 9 (thanks @ARiis-63) and at the time we recommended to simply disable UPGRADE_PARAMIKO on Rocky 9, which appeared no big deal as it already has a quite modern version by default. However, our recent SFTP benchmarks indicated various performance bottlenecks on Rocky 9, so we ended up revisiting paramiko upgrades to try out more recent optimizations - and they in fact turned out to yield significant improvements.
In the process we found the time both to confirm the reported issue and investigate further. In brief it turns out that mod_wsgi has subtle incompatibilities with the 4.3 version of bcrypt pulled in by the latest paramiko 3.x from pip.