I have found that in my process of developing survey123 surveys I have to delete folders quite often during testing. It seems that somehow these Folders which included HFS and Surveys get locked and I am unable to delete them for up to several minutes. Is there away to break AGOL/Portal folder locks so I can delete immediately.
There does not seem to be a consistent time until I can delete, it is random.
Are you deleting the surveys in Portal for ArcGIS from the My Content page or deleting them in Survey123 Connect? If the former and the Survey123 Connect app is open this may be causing locks. I suggest you delete the surveys in Survey123 Connect.
Hope this helps,