I think you have the right idea. It could be difficult to isolate the issue since the sector gear can affect the position of the cutoff. If you re-shimmed, try shimming the gears a bit higher or maybe try a stronger spring on the trolley. When I was first starting out, I was having issues shimming too low in standard mechanical switch systems, causing the sector to rub on the cutoff lever and not allow full range of motion. It would commonly block the trigger trolley completely or otherwise make a clicking noise if it was able to slip by OR just not allow the COL to engage the trolley at all and just shoot full auto in semi. At the time, I was having trouble getting good shimming on the gun (VFC avalon), so I opted for modding the trolley by sanding more of a slope on the surface that was meeting the cutoff lever so it could slide by. After this mod, it worked flawlessly, but this did not prove fruitful for me in another attempt, in which I opted to re-shim higher (Specna Arms Edge M4).