I came across this issue today for a survey embedded as a web form within a VUE js app:
"The webform needs to be upgraded, but an error occurred while upgrading." HTTP 504 Gateway timeout
The survey was published with Survery123Connect v. 3.9.120 to an ArcGIS Enterprise Portal and it appears that the survey123.arcgis.com api is "forcing" it to be upgraded to 3.12 and it is possible that the process timed out because of network speed.

The setting within the survey for forcing an update is turned off.

The only way to resolve the issue was to install S123Connect 3.12 and to republish the survey.
Is this a new "feature" of Survey123?
Is there anyway to stop survey123.arcgis.com from trying to force an upgrade while the user is trying to access the form? Is there another setting that can be modified?