Noise when changing level of individually routed loops

Hello, sorry if the first post is a support request. I use Loopy HD on an iPad pro 12.9 with iOS12.3 i have been using loopy for a while, I have set up in so each of the loops has its own individual channel in AUM. So far so good always worked flawlessly, I can add individual effects per loop, great fun.

Recently I started noticing a rustling/zippering noise when I change any loop amplitude level from the loopy front interface, similar to what you'd get on an analog desk with dusty tracks. I then increased the loopy latency and tried to cut down to only 6 tracks then one track individually routed but no difference. The only way to get rid it is to only use the main output in AUM. If you route even just one channel out you get the noise. The exact same thing happens in audiobus which I have also similarly configured.

In both AUM and audiobus I increased the latency to the max but I still get zippering noises if I route out single loops.

There is absolutely no noise if I just use the main output (standalone or via aum or AB) with twelve full loops running at the same time controlled either manually or via a controller (a midi fighter fyi).

Any suggestions? Thanks.