Hi.
I realized that the problem is the name of the bust files. The packs that were made for RPG Maker MV have the busts in individual files _bust_1, _bust_2, etc. If I change the file name to something like _bust, it works as it should.
Here are the links of the PVGames packs I'm using:
https://pvgames.itch.io/medieval-town-and-country-interiors-bundle
https://pvgames.itch.io/medieval-plague-bringers-diseased-town-bundle
https://pvgames.itch.io/medieval-warfare-knights-templar-bundle
https://pvgames.itch.io/medieval-high-seas
https://pvgames.itch.io/medieval-expansion
https://pvgames.itch.io/medieval-dungeons
https://pvgames.itch.io/medieval-underdeep
https://pvgames.itch.io/medieval-townsfolk
https://pvgames.itch.io/medieval-bosses
Thanks!