Rippling/layered FCP captions upon export

Hello Everyone,

I am having a huge headache here with a client's project which I am trying to send to them now. 

I have added captions to their video which are absolutely fine in FCP but when burn them in and I export them, they are layering and rippling in one section only on the playback o the exported version.

They are not overlaying in the timeline, there are no errors detected, I have tried to copy the project and added all the captions manually again....but still the same problem!! The previous caption flashes and blends in with the next one, intermittently showing the next and then the previous caption.

It is only in one section and it will not change no matter what I have tried. 

I have tried like an angry bear for a few hours to solve the mystery but I just cannot solve it!

If anyone has a suggestion I would be much appreciated as I could not find a similar issue anywhere else.

Thank you so much!