We just logged BUG-000123478: Previously functioning Survey123 Survey missing fields in most recent 3.5 release. What's happening is wherever 'pulldata' is used in the xlsx form, and the survey has several groups, some groups and questions are not displayed (iOS, Android, and Windows) with the latest version of S123, that were previously functioning. This doesn't appear to be happening to all surveys, just the really complex ones with groups and several uses of pulldata. I would hold of on updating. I'm not able to share any more specific details as the Survey in this issue is not public-facing, but if you have spare mobile devices handy, make sure you test your surveys with pulldata going on in them before updating all of your devices.
Joe C was the analyst that took the case and was able to repro within an hour with just one email, which was AWESOME! With folks like Joe at ESRI I have full confidence this bug is getting lots of attention and will be fixed soon.