I've seen various reports about this but nothign totally concrete. This never used to be an issue for me but as of the last maybe 6 months, I'm having constant sync issues when I export video from Premiere Pro...it's generally Iphone HD video, but the issue occurs with various settings in the export - if I use ProRes or HVEC 265 - if I do hardware or software encoding - and if I use High 10 and 2100 or not...I'm really not sure what's happening, and this doesn't happen if I use FCP instead (but I hate working in FCP). I'm going to post a dropbox link with two versions of the rendered video - one with the audio 2 frames forward and one in sync...because I'm always working with musical artists, the syncing is crucial. I'm starting to wonder if there's something wrong with my MBpro? I can even send someone the raw premiere files if they might be willing to check it on their end. I'm just at my witts end with this.
Perhaps the files with trouble are VFR, variable framerate? If so, converting those to constant framerate in say ShutterEncoder then replacing the clips in the project w converted CFR clips would help.