Unable to tell if this is a bug with AS or one of the testing mods. However, there is a slow crawl of memory usage going from 500mb to 1000mb. This will cycle very minute roughly before GC clears up the ram.

Likely sources are the packet or particle system. As both generate a lot of objects that could be filling up the memory.

Solutions: Create another object pool to store dead objects for reuse. As well to stop sending 100s of packets to the client every tick. This can be done by sending the raw data and caching it client side.

After doing a bit of testing this might just be Minecraft itself. Still very odd, without any mods it spikes up between 300mb & 500mb every few seconds. I think more testing is needed to see if a possible patch could be made.

New theory: AI and collision code.