Do you have a Condition Step between 3 and 4?
Try disabling the custom errors to see if you get more details https://learn.microsoft.com/en-us/power-pages/admin/view-portal-error-log
Also can try hooking up logging the errors to azure see "Enable Diagnostic Logging" in the same link above.
the GUID is the guid of the actual error so will always be different each time (if the diagnostic logging is turned on you should be able to find that guid in it).
If it is actually a system bug, chech what portal version is running, then double check if you have latest Power Pages Core installed, From Admin Centre select your environment then Resources->Dynamics 365 Apps and it should be in the list.
If a template issue (less likely) From Admin Centre select your environment then Resources->Power Pages Sites, then in the command bar Website Package Details
