Certain Mercenaries items bugged after lvl4

I’m doing raids in Mercenaries and making parties that sometimes completely evolve around a single item from one Mercenary. I raise that item to lvl 10-20 and then find out that it’s not working past level 4. My whole party is in some cases completely ruined.

Could you please fix that?
These are Mercenaries that have this problem as far as I know:

Thrall - Ring of Strength
Yu’lon - Jadefire Spear
Yu’lon - Serpent Pendant
Chi-Ji - Blazing Band

I’m sure there are more that need fixing. If anyone knows more, from first hand experience, please do tell.

A user here posted and updated all know bugs

too bad they don’t care so much