Hi James,
The connector was setup and able to see the surveys. After 2 days the Flows stopped running. I verified this based on the run time of the Flows and compared it the dates that surveys got submitted. There are no errors in Flow, it simply did not trigger. Unlike some of the other threads I am seeing on this issue I didn't have to recreate the connector however I did have to reauthenticate with the same Survey123 credentials. The connector was not in a disconnected state when I looked and in fact everything looked ok other than the surveys were not displaying. If I remember correctly the survey I have connected to was displaying an identifier number instead of the survey name.
Unlike Rogers issue below we never lost access to the Survey123 connector option. I am not experiencing any other issues like this with existing, non-Survey123, Flows. I don't think this is a token expiry issue given the short period of time between creation and the issue occurring (2 days). Additionally after fixing the last issue the Flow has been working consistently for the last 2 weeks.
The issue appears to be an authentication issue between Flow (opposed to the Microsoft tenant) and Survey123.
The Flow is currently in UAT and not been transferred to production over concerns that the system may not be suitable for use if it could fail without notice.