As an update Phil has been helping a lot with this and other nested repeat issues. They do now know it is an issue.
Unfortunately they are telling me that this will not be looked at, and hopefully addressed, until 3.12 - which will be at least next year. I hope more people post on this as it is creating a lot of issues for me.
I have a few work arounds to try.
Set appearance to minimal so it starts with 0 records and a +. But this is also broken in nested repeats so prob not for this case but it did help with some issues.
We have a relevant on one that asks did you collect this data? Yes/No. If you toggle from No to Yes back to No then Yes it will reset the repeat and go back to 1. Need to use a relevant on this.
In one case I was able to change from relevant to using the new body::esri::visible column and it helped.
Sorry I am not sure which one fixed which since I have been running into a number of issues with nested.
Hope it helps.