The plugin is very poorly coded, you shouldn't be using that at all. If you want an optimized and properly coded rank system, use the one that I recently made - https://forums.alliedmods.net/showthread.php?t=308540 - this one does the same thing, but it's 10x times better coded and has a lot of options to customize.
can you do something for this one because my players have level +100 and they don't wanna lose there level/exp.