I don't understand what you mean with "call all the bitmaps" and similar.
When you level_load a map, I think the blocks as well as their textures - which get freed on the next level_load call so you don't have to purge them manually - get loaded first, then entities and then the actions are executed, starting with the entity which you placed in your level first.

Going back to an older version where the error does not appear can be helpful but it is no guarantee that that version does not have a faulty file - still assuming it's not an error in your code or simply a missing file in your published folder.