Precisely! Lesson learned for me - test upgrades first in a lab. Also, TAC said they'd never seen our issues before so it may have been environment specific.
Creating a lab can be difficult based on time availablility, money, etc. In regards to the money issue, see if your SE will work with you on lab gear pricing. I've had success there. If you don't have the time to build a lab, maybe you can perform the upgrade during non-production hours to see if anything pops up. Our issue would've been seen immediately if we tested off-hours, but may not necessarily be the case for you.