Turns out this has been an issue for years that still hasn't been fixed. When using "multi-tiered threading" in replies will randomly turn replies to "hidden" even though they exist and are properly saved.
So, until we can get to the bottom of the code, I've turned off threading for this forum (which btw has now made a few of your replies visible).
Thanks to a member who reached out to me thinking their post got lost we were a Le to get to the bottom of this issue.