User preset keeps changing - burn in

I keep creating a new preset based on HQ108p but crucially switch the captions to none.

I have several videos queued and either when applying this preset or in the middle of the output process, some videos export with burnt in.  The number of times I have created a new preset only to exhibit the above.

Any ideas as to why?

NB: the videos also get exported low res with sidecar and this works fine.