Sure I’ve seen this on here before, I’ve posted at least once but it was not long after the group was launched (105/5800)
Every 12 months or so the bottom of the cage starts bouncing up and down with the chain miss-aligning on the gear, last weekend it involved the rear mech bouncing up and ripping itself off (through peddling force I admit….) and bending the rear hanger.
Checked all the usual, hanger straight, chain length, chain direction, indexing, everything you’d usually go through.
Is it a known fault?
Tempted to go Ultegra chain/cassette/RM this time around