So besides the off flavors, are you also having flow rate problems?
I actually don't detect any off flavors, and I do not have any flow issues. I attribute most of this to the bev seal ultra 235 tubing which has the really slick inner PET liner and forward sealing faucets (I have Perlick 650ss). The second thing I attribute this to is that I never leave a line empty after a keg kicks - I immediately put another keg on, and purge the line, so there is always liquid in the lines.
I have taken some of the faucets off when I pull hops from the keg and it clogs up the flow control shuttle inside the faucet.
The tubing shows no signs of any staining at all, which is pretty amazing.
I actually looked back at when I installed the tubing, and it was at the end of 2015 to early 2016, and I haven't cleaned my lines since then. I definitely think that is a testament to the beerline I'm using.
With that said, I do plan on doing a cleaning cycle within the next month. In preparation, I used a label maker and numbered all my lines. I've just been using the knowledge of which keg emptied to know which line to remove and reconnect - but when I clean half of the lines at once, I won't know which one is which without them being labeled. It is just a bit of an operation to clean the lines.