The exact from and to versions, 3-digit, would be informative.
The platform remained, I assume. Still worth providing its details,
server specs, web server, PHP, DB server programs and versions, etc.
What is this "resource"? Did Moodle create a course with that name and moved questions to its question bank? Was your earlier question bank at site level?
Did any notices, reports appear during the upgrade?
There were some question conversion/deletion processes which were advised/mandatory before the upgrade to 5.x the latest. Do your admins know these?
There are all kinds of health checks around the quiz system, yoursite/admin/tool/health/ for example. I don't know offhand, hope others will rhyme in.
All in all, what your admins have started, they should finish. They can of course ask here directly. Through this change of hands, information gets lost.