Audio going out of sync on export

iMac M1 with latest Sequoia, latest version of FCP.

2 audio channels in project: 1 attached to video from lavalier going directly into Sony FX30, the other from a condenser going into Audacity recording my instrument.

The lavalier also picks up my instrument sound of course.

All sample and recording rates seem to be in line (see photos)

When monitoring within FCP audio will be in sync, but when exporting to either full-size default or "Apple 4K" or HEVC, some parts of the audio will go out of sync, causing an echo-like effect

I have searched and tried many things without success

Thanks in advance for your advice