Does anyone experience issues syncing sound recorded outside the DJI app using OSMO?

Can anyone tell me if there is a way to overcome the DJI Osmo mobile shooting variable frame rates? When I shoot with my iPhone and the OSMO, and record sound with my sennheiser radio packs, the sound won't sync....any other scenario, the video syncs fine....If I shoot just iPhone (no OSMO), if I shoot with my nikons, If I shoot with my iPhone and my lanparte stabilizer....no problem syncing sound recorded with my body packs, but as soon as I shoot using DJI software and OSMO....the only way to SOMETIMES fix the inability to sync sound is to use handbrake to modify the vid into NON variable frame-rate----although this does not always work.....this means for pro shoots, I can not trust the OSMO (which is sad, because it is otherwise a great rig. )

ANY EXPERIENCE WITH THIS ISSUE?

Michael, can you provide the original video? Thanks for your help.