Cutting the a small portion will not do anything to fire resistance, I believe, but there is regulation. You probably need to check with Bomba. Maybe they can advise you. I think it has something to do with gap around the door frame. However, in this case the gap will be closed back again by the flooring. It should be fine. The bottom side is less stringent.

Just call Bomba to get guideline.

They probably just heard what other say but did not know why    If the Bomba can give green light but the management say cannot, then cannot also, right? Unless not stated in agreement. However, if you can get black and white from Bomba, no one can argue