I’m starting to believe real-time weather might be causing this sometimes. Not because there would be times when weather conditions would be so complex it would drastically bloat memory or resources, rather, because the data coming from the weather servers would be hill-formatted and causing FS2020 to choke on it.
Otherwise there is another issue related to FS2020 spawning hundreds of seagulls and other fauna 30nm away for example, and this one is very nasty because there is no visible indication this is happening:
https://forums.flightsimulator.com/t/seagull-model-causes-massive-fps-drop-when-loaded/309427/12
PS: I didn’t try disabling seagulls yet.