Thank you for the videos and audio. All this is reiterating the fact that the high side is not tremoloing the audio, and the low side is. If the high side was working correctly then your Quaverato would sound just like the one in the videos.
There is almost certainly not a problem with the pots, but you can test this by measuring the voltage on the center pin to see if it’s getting from 0 to 5 volts. The transistor is not bad because you are telling me the high LED is pulsing. If the transistor was bad then it wouldn’t work. We’ve already established that the LDR is working, at least somewhat. You can do some more tests to ensure that the resistance of the LDR gets up to at least 1M ohms or so when it is in complete darkness. Right now, it seems like the only potential cause for this is that the high optocoupler is not sealed well and is letting some light in, causing the resistance to remain low across the LDR, so it never gets to compete darkness (up to 1M ohms across it). But i’ve already asked you to seal the optocoupler well and i’m assuming you’ve already done this.
You can test the optocoupler (with the power off) by measuring the resistance across it’s pins in the darkness. You can test if it’s sealed well by shining a flashlight on it to see if the resistance changes. The resistance should get much higher than 1k7 ohms in the complete darkness. Test both LDRs this way to ensure they are both behaving the same.
-Brach