Before stat squish, I really only had an issue in the lead up to the final quests of 2.0. And I don't do the roulettes on any kind of regular basis or any extra content.

I leveled an alt to level 80 after the release of 5.3 as I wanted to experience the story trim to see how things were different. I only had issue in the 47-50 area. Once I got to ARR patch content, I had no issues with levels whatsoever.

I haven't leveled an alt in that range since Endwalker released so I can't say if it got broken or not, but given how far into Endwalker we are, it would have been something mentioned by now so if you searched and didn't find anything chances are there's something you forgot with regards to your experience that's caused the issue.

Do you remember what experience level you were at when Endwalker hit? You said you were aware of it, but didn't mention where you left the experience. If you left almost a full level's worth of experience on the table, that's probably a pretty big portion of what's causing the issue. Especially if you aren't doing non-MSQ stuff like roulettes.

How many classes are you leveling up currently?

If more than one, could you have accidentally done a final quest mission click on a different class by mistake giving experience to the wrong class?