We have recently upgraded to Moodle 4.3 from our previous version 3.1 that has been used for many years. We were performing the upgrade gradually and everything was fine till the 3.11 version. Since the 4.1, few courses were not upgraded properly, returning the following error: Exception – Undefined constant „ASSIGN_EVENT_TYPE_DUE“. Now in 4.3, we try to bypass the problem by creating new courshells and restoring the content from old backups, with omitting calendar events and legacy course files. In some cases, this solves the problem, in some it does not.
For these corrupted courses, even created as brand new in 4.3, there is no way to access them for any user, no matter the system role. The only thing admin can do through the course management is to create a course backup or restore it from backup, by deleting the previous content. Teachers who are assigned to such corrupted course will receive the very same error message - Exception – Undefined constant „ASSIGN_EVENT_TYPE_DUE“ when trying to open their Moodle home page or Moodle Dashboard. What is absolutely weird that some courses, created in 4.3 and restored from older backups were first fine and after several days, they got corrupted on their own, showing the same error (no user made any updates to course content nor course settings).
Have not found much information on this error. The only thread where this error is mentioned is back from 2017 https://moodle.org/mod/forum/discuss.php?d=353347#p1426752.
Any suggestion what may cause the issue in 4.3? I assume there might be included some assignment, perhaps with very old due date. Nevertheless, I am surprised such an issue disables the whole course and even the dashboard. If there is anything I can specify, let me, please, know.
Thank you for any advice on this one.