What happens if you upgrade from < 3.8 to 5?

[TechForum]

I recently upgraded from 3.7.1 to 5.2.5. I didn't encounter any problems during the migration. But I can't login to the forum as the admin through the regular login prompt (it hangs). Although, /admincp lets me login as admin. Also I am having problems with mysql crashing frequently, but this could be because I switched to a virtual machine with fewer resources than before.

But my question is what happens if you upgrade to 5.2.5 from a version prior to 3.8? If there's a problem would it be obvious? Or are there hard-to-diagnose problems that occur if you upgrade to 5.2.5 from, for example, 3.7?

tl;dr
What are the actual problems that can occur if you upgrade to 5.2.5 from a version prior to 3.8?
Thanks!

[In Omnibus]

Do you have a database backup?

Any version of vBulletin 3 from version 3.6.0 and newer. If your vBulletin version is older than 3.8.0, it is recommended that you upgrade to at least vBulletin 3.8.0 before you can upgrade to vBulletin 5.

https://www.vbulletin.com/docs/html/upgrade

[TechForum]

I do. I was just curious how the problem of upgrading from < 3.8 to 5 manifests itself. Is the problem complete failure? Or are there little problems hidden in between?

[TechForum]

I just tried again, this time first upgrading from 3.7.1 to 3.8.9 and then to 5.2.5 and now I can sign in as admin! So if anyone else has a problem signing in as admin after upgrading from < 3.8 to 5.2.5, try upgrading to 3.8.9 first.

[BirdOPrey5]

Thanks for the feedback. We do suggest people upgrade to the latest 3.8 being continuing on. Out of curiosity when you could log into the AdminCP but not the main forum, did you attempt to change your password via the AdminCP?