Sounds to me like your burning out the nervous system and not the muscles. The nervous system takes far longer to recover from. Don't go to failure and train with less reps per set with lots of rest (ala GTG) or build your base more with some 24kg KB work.

All out single sets with the heaviest weight you can use all of the time will get you nowhere - besides maybe going backwards or getting injured.

Sorry, but I don't believe you when you say that you aren't training to failure on your single sets. Otherwise why would it be 1x8 reps right and 1x6 reps left? You only see that when people are pushing the envelope.