I assume your native language may be German, so you may want to have a look at the German Drucktipps3D forum for the J1 riser thread. My own design included 
Very nice investigations!!! and it’ so easy to fix it without any expense! As you described it, I remove the washer from the filament sensor and add a washer on the lever tensioner. SInce then no more issue during printing!! no noise, the filament is well driven in the bowden tube. I can do awesome print.
I printed PLA, mixing PLA+ and the snapmaker Orange. All prints are now successfull.
many thanks
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This is how I think about my problem with clicking when trying to feed filament. A few days ago I bought 1 set of BondTech 1.75/5.00 gears. I haven’t installed it yet. I looked at the construction of the assembled head and this set. Namely, when I put both gears vertically on a flat surface next to each other, you can see that both gears mesh. However, as soon as I moved them apart to the width of the filament (1.75mm), the teeth of these gears no longer cooperate so well. Filaments are different, more or less precise in terms of dimensions. Not to mention the shape is also not always straight and round. As I mentioned earlier, the clicking occurs differently. Maybe I just hit some bends or a larger diameter and the teeth start to slide between each other, which causes non-meshing and a specific clicking. Despite the spring used, the pressure force is too low for the cut grooves to properly penetrate the filament. In my opinion, this is a good solution for soft filaments such as TPU, but PLA, PETG, ABS are too hard and too smooth for this set of wheels to be able to push the filament.
I also own the A250 model, received for support on Kickstarter, with an additionally purchased V2 head. The filament feeding solution there is completely different than in J1 (possibly also J1s). A small wheel with sharply cut notches cuts into the filament, and the semi-circular wheel only presses.
These are just my thoughts and conclusions. I may be wrong.
Does anyone have a good solution to the problem?
Most commonly the complaint seems to be with trying to print PLA, and quickly. The general understanding is minor heat creep, detailed here and in another thread.
All-metal heatbreaks have been found as a general solution. Either homemade modification, or Snapmaker now sells all-metal, single-piece hotends that seem just as well.
Many other things have been suggested as improvements including the extruder gears, a straighter filament path, and other things. I tried them all, but only all metal heatbreaks solved the frequent, intermittent skips for me.
Snapmaker reached out many months ago to the community and any others that may have been affected by this.