So maybe slightly fatigued /worn/twisted/knocked hinge bit.
“New” big cassettes, 46T or more: independend from the make of the rear mech – have the imression that they don’t last as long any more with those cassettes.
Old XT rear mech – only used with 3×10 and 11…36: no “torsional play” at all (when I grab the rear mech and twist the thing around the vertical axis).
When using these wide range cassettes, rear mech after 1/2 year of intense use: still shifts o.k.. But significant “torsional play”… Spoke with a guy from the LBS about it – he confirmed this.
If the wide range cassettes are harder on the rear mech and at the same time you need better tolerances due to more gears … this might create problems quick.
Guess the times where an mtb rear mech was lasting more than 2 years of hard use is over.