by Ken Task.
What is the specific build date of the prod and of the qa?
Found in version.php file at the root of moodle code directory.
2.3.1+ could have two different build dates and thus not really the same exact code - thus the error shown is correct.
BTW, both are probably in need of upgrade to the highest/most secure 2.3 which is now 2.3.8+ including some newly discovered security updates.
If using git, git update both on the same day and then they will both be of the same build date. ;)
'spirit of sharing', Ken