Bit of an odd memory usage pattern. Typical is a sawtooth. A healthy sawtooth tends to ramp from 40%-ish (or less) to 80%-ish, then GC knocks it back down.
Except. Long time spans for requested graphs, especially in the reporting module, randomly spike memory. A couple or more such requests together could push a server over the edge. Perspective also loads a server much more than Vision, so a bunch of busy clients can do similar.
Consider this similar topic:
Maybe also set up GC detail logging in ignition.conf. See how long your pauses usually are.