Skimmer Fluctuating

[Arok3000]

I don't know if you checked it when you cleaned it, but mine does something similar about every 6 months.
Inside the venturi fitting, at the air input part, but in a really hard to reach place, I get salt buildup that impedes the flow of air sporadically. My bubbles will collapse, I'll adjust it, then they'll overflow with a bit more air, then I'll adjust it back. It drove me nuts until I eventually soaked it in vinegar and used a little pick to clean out the salt.