Un-charted territory for me. :|
bigbluebuttonbn became part of core in version 4.0 of moodle
https://moodle.org/plugins/mod_bigbluebuttonbn
as an add-on-plugin:
https://moodle.org/plugins/mod_bigbluebuttonbn/versions
shows a BBB version 3.0.9 for Moodle 3.11
and part of a set:
https://moodle.org/plugins/browse.php?list=set&id=2
mod_bigbluebuttonbn and mod_recordingsbn
You said:
"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“."
Error suggest something to do with calendar and mods/assignments due.
Suggest restoring your 3.11 sql dump to a new database.
Then query that database for anything related to BBB and courses that used it. Can't tell you what issue would be, but you know the course ID's that are having issues right now so concentrate on those. Moosh might be handy as it has a command for course info and backup info.
Comment: have never been in favor of hyperjumping. Using git for moodle core versioning takes the pain out of hyperjumps and one can march a moodle through each higher version farily quickly. You might catch exactly where the issue begins and address it at that point before upgrading further.
'SoS', Ken