I can confirm this problem on my/our 2 different Nord (European Model).
If the intensity slider of the night light is on the far right, it works quite well, but it doesn't work if it is in the middle (default) or left.
I also read a news report a few weeks ago, it was probably in the XDA News Portal (www.xda-developers.com), that many phones with in-display fingerprint sensor have problems with reading the fingerprint when a custom ROM is installed and the night light is on.
I cannot find the article at the moment, but I will search for it.
Nobody else has problems with fingerprint reader and night light ?
Ok I see what you mean and I'm also having that issue. Will take a look about that. Thanks for reporting.