If I’m not mistaken all of your pedals are floor pedals, which generally are not line level effects. Line level is a hotter signal level (compared to consumer level, which is where most guitar floor pedals are at), and requires line level effects to work properly. In most cases that means rack units, though I’m using the Eventide TimeFactor for delays, which happens to be a floor unit that is switchable between line and consumer level. Unfortunately, the line level loop limits you in that sense, and I don’t know of any workaround other than getting the amp modded. But this would explain why you’re getting a level drop with your pedals in the loop, and why most likely you’re hearing a distorted signal from the first pedal in your chain being overloaded.

Now that you got me thinking, maybe there’s something out there that can take a line level signal and step it down? You could put that first in your effects chain and then finish it off with a boost?

By the way, the Framus has a parallel loop, so unless you want to hear 100% effects, you wouldn’t want to turn the loop all the way up. There’s a slight boost if you set the loop level to 12 o’ clock, and that where I keep mine at.

Hope this helps!