Big loop handle on Marlin 1895 45-70

I purchased a black loop lever for my Marlin1895 45-70 rifle.  Today it start getting loose after firing 5-10 rounds.  The medium size loop lever does fit and locks in but does not stay locked in after firing rounds. It does uplock pretty easy.  Has anyone had this problem before?  Maybe it does not fit securely enough, any easy fixes?