>>1565636Possible reasons:
>1. Shift cable has stretched, is breaking/about to breakThese always break up at the shift lever. Pull back the hood, and look in there with a flashlight for broken strands. With the R8000 and similar levers, with the cables buried under the bar tape, you definitely want to catch that before it breaks all the way because it's a massive pain in the ass to remove the broken remnants after that. If your rear shift cable is routed outside the chainstay you should unhook it down there so there's slack in the cable so you can try pushing the cable out of the lever to get a better look at the state of the cable.
You can also just pull on the derailleur while turning the cranks when it's like in your pic and see if it shifts to the larger cogs. If it does then it's a cable problem for sure. If it's not breaking at the lever then something is breaking somewhere along the line.
>2. Derailleur Low Limit is severely misadjustedThere's two adjusting screws on the rear derailleur, marked 'L' and 'H'. It's not unheard-of for them to mysteriously get massively misadjusted. Unlikely it's misadjusted this bad but possible. If you look close you'll see where the end of the adjusting screw butts up against the moving part of the derailleur; if there's no gap when the derailleur is like in your pic then it's misadjusted.
