I have an Ultegra R8020 lever and I recently did a cable change. Everything worked fine for a few moments then on the first ride the left shifter wouldn't click up into the big ring. After a few attempts it crunched into place. After investigation I found that if you ever so slightly touch the paddle to shift down gear then the upper shifter will not work. This isn't the same on the right hand shifter which shifts fine.
I've taken the lever and hood off, degreased, greased and it works slightly better, but it feels like a mechanical issue instead of dirt or grit stuck in there.
Are there any tips on how I could rectify the problem? The shifter was in otherwise good condition before the cable change. It is nothing to do with the derailleur or cable, I can confirm its the shifter that is sticking.
Thanks for your help, Brad