by Ken Task.
Just how are you seeing that mod_chapter thang is being changed when 'backup runs at another location'?
Am not understanding ...
Backups don't change content. So is it the 2.4 version 'backup' that's showing/doing something in the 2.7 instance database? Or vice-versa 2.7 -> 2.4?
What sort of additional plugins do you have installed that could cause interaction between Moodle instances?
In the one example you give, is the mod_book_chapter ID XXXX resource available in say Moodle A ... and someone copied a url to that mod_book and used the URL in Moodle B?
Are both of those instances using the same authentications or some sort of authentication where by moodle user X logs into the 2.4 and they are also logged onto the 2.7?
Comment: but don't upgrade yet .... both versions you are running now are quite old and haven't gotten any fixes to code nor security updates in a while now. Suggest that after this current issue is at least known as to how/why it is happening, that both instances be brought upwards to a supported version.
How about some specific technical info ... we know version numbers of the Moodle's involved ... what about other stuff ... Operating System is? Hosted how and where? PHP version? MySQL version ... etc.
'spirit of sharing', Ken