There’s some peculiar thing going on with asset replacement hierarchy - somehow entire _strm_ mapdata files unload in some very specific areas, and mostly related to fwy_01 in downtown_01.
This looks like it fixed it at one point, but all it did was move the issue further along, as that code had a typo, so the fix for that typo probably regressed mpheist4 DLC hierarchy again.
The weird thing here is that mpheist4 has no replacements for any base map assets, so it can’t be some issue with incorrect streaming extents loaded from GTA cache.