Github branching strategy


This might be documented somewhere but I haven’t been able to find a good answer to it.
I was looking at the 4.22 branch on Github and I was wondering what it would take to merge that into my 4.21 branch.
When doing a quick merge to just check the possible conflicts, I noticed it chose a commit from 5 months ago as the base instead of the final 4.21.2 release commit.
After taking a closer look, I noticed that at some point, changes that were being made in the 4.21 branch were being **redone **in the 4.22 branch instead of being merged which becomes quite problematic for Git.
Has it always been like this? Is this a side-effect of Epic using Perforce on their end?
How have people been going around this?