I have the same issue. SPT 3.9.8 with only SAIN + DrakiaXYZ-BigBrain + Waypoints mods.
This looks to be the same issue as thread #5085
I did some digging and it seems it has something to do with the stash size.
I have level 2 stash and the errors are thrown for items which are placed on cells with y = 29 ~ 36 (lines that belong to level 2 stash)
so if I move the items higher in the stash and also free up some additional space and then buy something, I no longer get this errors (did a profile backup previously).
Somehow the stash size is not processed correctly. I think it's because the level 2 stash (id 5811ce572459770cba1a34ea) is defined with size 10x40 in SPT_Data\Server\database\templates\items.json but is defined with size 10x38 in EscapeFromTarkov_Data\resources.assets ("cellsH": 10, "cellsV": 38, )
