Can you take a look at this post: Memory leak/GC issues in ignition gateway 7.9
(where apparently the forum move deleted all my screenshots, but the graphs were the same as your graph here)
In my case, it wasn’t a memory leak, but the garbage collector taking too long to kick in and subsequently taking too long to clean everything up, stalling all threads in the process.
Switching to the G1GC garbage collector saved the day as that cleans up in smaller parts, causing shorter (even unnoticeable) stalls.