We've recently upgraded AEM from 6.5.5 to 6.5.7 (didn't install 6.5.6) - running on Ubuntu 18.04.5, Java 11.
We have been pretty consistent the last 8-9 months after making some performance adjustments in migrating from 6.3 windows to 6.5 Unbuntu. Rarely having to restart. However, since we've upgraded from SP 6.5.5 to 6.5.7 (we bipassed 6.5.6 - which SHOULDN'T matter), we've noticed really poor performance, author instance needing restarts nearly every 2-3 days and publish instances 5-6 days because of becoming unresponsive. No heap dumps or OutOfMemory exceptions.
I'm just wondering if anybody else might know of any obvious reasons this could be happening before I bog myself down in a sea of heapdumps and threaddumps.