I've an SH86 which is the same but comes with the vacuum bag never had any serious problems with it and liked it so much bought a second one to save changing the tubes over. Only have two problems with it as a vacuum occasionally pick up a small twig which can get stuck in the fan and if vacuuming leaves from a path and there is dirt under them it will pick up the dirt which if damp will build up in the curved tube and when it dries it will come loose and and jam the fan. Tubes can be a pain to take off. Happy with Stihl and have a BR600 and 800 for bigger jobs.
Maybe I just got a bad one, but I had just come off a really good experience with a cheap Ryobi blower/vac that worked great for about 15 years, so I incorrectly assumed the premium Stihl would work better, and I was disappointed because it was much worse.
I used it mostly to blow leaves, and it did OK for that. But in the fall I used it to vac up leaves that get stuck in the corners around my house and in the flower beds. It had all the problems you describe with clogging and jamming and difficulty changing over. On top of that It really didn't have good suction if the leaves were wet. It did fine on perfectly crisp dry leaves, but we rarely have those.
The worst part was that it just wasn't made to handle leaves and debris that comes with them. When you vac leaves you get other stuff - twigs, seeds, the occasional pine cone or acorn. It has a little metal grinding blade in front of the plastic blower wheel, but I couldn't tell that was doing anything. I replaced the blower wheel when it disintegrated twice and when I couldn't JB weld the holes and cracks in the front blower housing anymore I replaced it too.
Then I bought the 36 volt Makita battery powered blower and used them side by side and the Makita blew as good or better than the BG86. It was always a pain to start so I gave it to my landscape guy and haven't missed it for a moment. I've had pretty good Stihl chainsaws, but I can't recommend that blower, sorry.