Usually the problem presents itself as follows:
Mission start, loading is slow and stuttery. If the game manages to load scenery and textures, problem sometimes does not occur immediately at mission start.
Prior to the problem occuring, game shows severe symptoms such as textures not loading on random objects while they do on others, LODs not loading on some objects while they do on others, movement inputs becoming delayed, animations not loading (causing characters to "slide" around rather than walk/run) and physics simulation problems causing vehicles to shot away from objects once simulation catches up, probably due to physics boxes intersecting each other during loading lag.
The game exhibits this problem every time some asset needs to be loaded, including sounds, muzzleflashes, tracers, voices, animals, etc, etc. Lowering texture and object quality does not alleviate the problem completely. Neither does moving to an easy map such as the VR World.
Individual objects can cause these lockups. For example, placing a tank previously not loaded in the VR world and then jumping into the game causes the game to sometimes get stuck on loading texture and/or model, freezing up the computer.