Noise reduction suddenly stopped working

Windows 10\64 Audacity 3.2.4
Any suggestions will be appriciated. Been using Audacity several hours cleaning up and EQing 5 minute audio (MP3) files. All of a sudden Noise reduction has no effect on files. Getting sample and then selecting entire track then applying. No change in background noise level (low room fan\ac noise - approx -42db). Suggestions? Thanks in advance

So I just check Noise Reduction on 3.2.4 on my Windows machine. It seems to be working fine. Note the 12-6-3 seemed to be more effective for my particular test than the 6-6-6.

Perhaps you want to post a sample of the .WAV file that you are having difficulties with.