I don't know much about the ruletile asset, but this is what I usually do for tilemaps:
- Create assets at all the same size in the same file, power of 2 sizes (Which it sounds like you did)
- Import the asset, set sprite mode to multiple, open sprite editor
- Slice by grid size (Which it sounds like you did)
- Create the tilemap with a tilemap collider and a composite collider. Check the option in tilemap collider "Use by composite." This causes the tilemap to become one large collider instead of many small ones, and I'm hoping this solves the problem.
- Add asset to the palette and build the tilemap.
Also, I noticed your character is getting stuck on walls. You can add a physics material 2d to your character with zero friction to allow the character to slide on walls.