This is a new Microshift Centos 10sp controlling a Shimano 105 rear derailleur.

This used to work not long ago with me being able to accurately shift from gear to gear, including multiple shifts in one go.

Now when I'm downshifting the shifter skips indexes and on the rear the chain thus skips cogs. I can even feel the front right shifter go through more than one index. When pressing down on the thumb/down I can sometimes feel it go one index down, sometimes it'll go three or even more. This isn't a full and deep press the way it's supposed to function, this is me pressing as gently as I can to trigger only one downshift.

It appears as if there isn't enough "traction" or "resistance" in the shifting mechanism for the index to hold its position, so it slips. Even after upshifting the chain moves appropriately to the correct cog in the rear as long as I maintain the long paddle shifter in the 'activated' position, but as soon as I let go of it I can literally feel the index move down again.

(With the shifting wire disconnect, i.e. with zero tension, it will shift naturally, step by step or in multiples as I wish. With a moderate tension from me pulling on the wire firmly it again works fine. But not with the cable attached to the rear and set up).

So, again:

- I know it can trigger multiple downshifts, but that's not what I'm doing or trying to do, I press gently
- I know it's skipping indexes because I can feel it
- I know it used to work so it seems the rear is set up properly

What I've tried:

- Changing cable tension
- Changing derailleur position ("up/down")


Any thoughts here?