Good to see you have found the cause of the issue, as a side note, all 9100 will still be in warranty if you do have a parts failure; Shimano Dura Ace/XTR has a 3 year warranty, and as this was only introduced in mid-late 2016, so even the earliest sale parts will still have at warranty till mid 2019
https://bike.shimano.com/en-US/infor.../warranty.html