Load frame in background

You could make a level generator that stores all of the active objects in the level in an array or list,
and then load (create) them in small chunks at start,
1 chunk per frame,
since chunks amount would be predefined (i.e. number of rows= frame height/32)
you can make a progress bar showing current row loaded among (frame height/32) total rows

Another possible idea you could try
(not 100% sure would solve your issue, as it depends on how your level is composed, but it's simple enough to try)

1) insert a new frame before your "game" frame, and place in this frame single copies of all the different active objects you are going to use in the "real" frame
2) untick "create at start" from all of these objects
3) create single objects one by one, one per frame loop, and display all of their animations/directions if applicable in subsequent frames

this should load all needed graphics before the next "official" frame, and so relief that "freeze"