Here is an outline of what I found and posted on Discord…
You mentioned checking scales, if you changed any, a re-unwrap and re-export is required to fix the issue when importing to InstaMat.
Check your Normals too.
The UV’s show no obvious error, however it looks like you have mixed up the mid poly backups and the low poly models.
Move the mid poly objects to the low poly collection and the corresponding objects to the mid poly backup collection.
Remember: After making changes in Blender you will need to re-unwrap and re-export before going back to InstaMat and re-importing.
let me know if this fixes your issues.
