I have a massive form but I was able to recreate this situation even on a simple form.
You have a group inside a repeat
The group has a relevant on it based on a calculation field
Inside that group is a Required field
If you are on repeat with the Required field showing it will always trigger even when the field is filled out. If you go back to a repeat that does not show this field it will submit. So say you have a field that shows up every other repeat. If the form is sitting in the +2 repeat it will never submit. If you go back to repeat 1 and submit it works! No changing of values or anything. It is like it is seeing it as '' when you are on that repeat.
See attached form. Bug is in 3.3 and 3.4 beta.