Map can't load...size problem?

Thanks for your answers, guys. I feared as much... guess I'll have to reduce my map sizes then or split up 1 huge map into 2 smaller ones, but that will use up the few remaining unused tilemaps even faster now.

Edit: alright, after bit more playtesting I don't think anymore that map size is actually the problem. I've reduced my maps to 2048 x 1024, which is also used with some maps in vanilla, and for L2 tilemaps an even smaller size of 1024 x 1024 is actually sufficient, but the issue of the map not loading and the game either freezing or crashing remains. I've been using the following tilemaps which are unused in vanilla:

2C, A8, A9, F5, 12A, 12D, 12E, 15E, 15F

They are distributed in my maps like this (I'm only using the first two layers, didn't need the third so far):

Map 1: 2C (L1) & A8 (L2)
Map 2: 15F (L1) & 15E (L2)
Map 3: 12A (L1), 12D (L2)
Map 4: A9 (L1), F5 (L2)
12E as reserve


Map 4 with tilemaps A9 and F5 loads without problem, but the other 3 always crash the game. Then I started experimenting a bit and exchanged tilemap A8 (the layer 2 tilemap of map 1) with tilemap 12E, and all of a sudden it worked! The game now loaded the map normally, despite the two tilemaps A8 and 12E being identical. So it almost seems like the game doesn't like certain tilemaps, and perhaps that's why they went unused in vanilla? Either that, or there's definitely something buggy going on here... Can individual tilemaps somehow become corrupted?