Well writ, Pulykamell. The issue of “edge flashing” was pandemic with Holgas and to some extent with other daylight spool loaded cameras. This was not limited to still cameras either. The 100 foot “daylight spool” loads of 16mm film commonly used in Bolex or Arriflex M or S cameras were also prone to flashing along the edge of the film if one were dim ( heh ) enough to load/ unload the camera in direct sunlight and were to pull the spool too firmly when disengaging.
I’m curious to see the negatives too. “All brown” makes me think they are color negatives not black and white, and are 100% exposed. They’d be clear but brown-colored, the prints would be black or very darkly blackened. Is this the case? Even before you scan them in for us, can you articulate what a print looks like a bit better?
The way to find out if your lab is wrecking the rolls is to waste a bit of money. Take a brand new roll of 120 film tear off the tape, then send it to the lab. Don’t shoot anything on it. The negative should be properly developed, and the photographs will come back completely white. ( Solid negative equals total absence of light equals white prints. Clear negative film base with no emulsion left on the film due to exposure would equal completely black prints. )
A moment of wistful remembrance. When I was teaching the Steadicam Workshop in the early 1990’s at the ( much-beloved and mourned ) International Photographic Workshops in Rockport, Maine, the school store got in a shipment of Holga cameras. Now, at the time this puppy was something like 9.95 for the body. Seriously. I and a few other medium format afficionados were ballistic with glee. A ten DOLLAR camera that shot 120?? Who knew? I got one and a pile of film. It was good for a lot of laughs from the 35mm movie film camera body snobs in the class that my dear pal and co-instructor Kenn and I would run around screaming, " Where's my Helga !?? I must shoot this moment " while surrounded by a cool 3/4 Million in Steadicams and film cameras. Rue the day I lost that body.
Indeed, they were infamous for light leaking. I know that rather than embracing that aesthetic ( which was of course utterly unpredictable ), we’d do the right thing and load in very subdued light, and use black paper tape to seal the seams up. Still, the lens was a piece of crap disk of plastic and man, the atrocities of optical impurity did indeed yield some beautiful results. Some were VERY 1880’s in appearance… Miss that camera. If one is curious about what these shots look like, go to Google Images and type in " Holga images " and hit enter. A long page of Holga shots appears.
I know of the Lomography store and movement and am sorely tempted to get a Holga again. Their Spinner 360 is an absolute delight to use.
Please do share a few of these images. We will help you figure out what’s wrong and try to guide you towards enjoying your Diana !
ETA: Oh ! One detail may help you here. I seem to remember that the Holga has you load the 120 roll of film sheathed in its paper light-proof backing, and as soon as the take-up spool has engaged, you close the back up and shoot. Yes? When you are shot out, you use the mechanism to release the gearing and re-wind the film back onto the roll, or do you take it out once it is shot and remove the take-up side? Perhaps you’re opening the door inadvertently or the door isn’t latching properly and as you handle the body, light is flooding the film. Having to re-wind exposed film back onto the original feed side spool would cause more light leaks onto the film, if you are indeed suffering a badly locking back panel. Do you rewind after each roll, or just wind FORWARD until you hear the paper end flapping, then open up and remove the finished roll?