I ran into a similar problem when trying to sync an MP3 from Audacity with a MOV file that was exported from Lightwave 3D animation.
https://forum.audacityteam.org/t/mp3-from-audacity-out-of-sync-with-30-frames-per-second-mov-animation-in-filmora/55550/1 (Scroll to bottom of thread to see the final solution)
For some reason, Lightwave 3D misinterpreted the number of frames in the MP3 file, which threw off the timing when used as a reference for the lipsync. The solution is to use a WAV file instead. I don’t know if an Audacity-generated MP3 file is somehow different, or if the format itself lends to sync troubles, but it’s possible that the MP3 is being misinterpreted by your video editing software.