"GMRoomPack tries to find room's each layer by name (via layer_get_id), and, if there isn't one, creates it at the original depth."
So if I made sure that packed room and room in which packed room is loaded to have layers with same names, the "layer_get_id" would work properly?
Currently instance layers have different names - "Instances" and "sort_begin".
"As of issue #1, are you loading multiple tilesets into the same room? You might need to store the actual tilesets into a separate list (and loop over them) but it's hard to tell with this little context."
Yes, I'm loading 2 tilesets. What else do you need to know?
"Needless to say, this makes issue #2 a bit mysterious - perhaps you are loading a room with another controller object and GM declines to create duplicate layers? I'd suggest to try logging IDs of your grid layers."
Okay, I'll do that the next day.