Although the login is successful, the members see a page with a red "something went wrong". By refreshing the page, and in extreme cases by going to the homepage, everything starts working again. The error log is replete with:

RE: Array ( [error] => httpServerError [error_description] => Invalid grant: authorization code has expired )

Grant authorization time is 30 seconds. It would be impossible for the grant to have expired during login (3-4 seconds max). The date/time on the machine is 100% accurate. 

Please advise.

With kind regards,
Michel

What is the OAUTH login provider interacting with? Are both systems rendering the interaction correctly and within the given timeframe? 

@Jim M,

Apologies for the delay. We have our own OAUTH2 provider and we used it successfully for many years before without any issues till the May 8th update. It seems that this issue is not only isolated to us. We have the same issue as outlined here:

https://invisioncommunity.com/forums/topic/474829-issues-with-integrating-custom-identity-provider-service-to-an-invision-community/