Face ID not working in low Light

I have a client who recenlty had her screen replaced by someone else and is having face ID issues after which. I deducted that Face ID working great in good light but not at all in low light. I do not know what could be causing this issue. I do not want to reccommend repairs that i am not sure of since i cant say for sure what the issue is

Any help is much appreciated!

Thankkkssss!!