Are the missing tracks muted in PP at all? Were they ever?
Sometimes a project can be weird/corrupted and do strange things. Then you need to outsmart the computer. For example, try an audio-only export. Create a .wav file and import back into project, and if all tracks are properly represented in that mix, add .wav to timeline, mute all other audio tracks, and do your final AV export using that new audio.
Safe Harbor Computers