The Swiss CAA is saying so.
Just one data point: my local club in Egelsbach has had to completely ground its fleet of two BR23s more than three months ago (a huge financial disaster by the way) due to exactly these mentioned symptoms. By the way, these aircraft were always operated on 100LL or UL91 only.
Rather surprising as the carburetted Rotax 912 has been around for many years.
Sounds a bit vague to me.
There is a recent SB related to a faulty batch of stators. It does not describe the in-flight consequences of a failure of that part and I have no idea if power loss or rough running could be one of them. The serial numbers of the affected engines are higher than mine, so the prob40 a production issue that started late 2020. Again, just saying, no idea if this could be the issue.
Interesting @Boscomantico that these two B23 had the same issue while using 100LL and UL91.
That seems to be across much of the range of Rotax engines.
It would be difficult fto compare experiences here with that of your B23s as most Rotax engines based at LFFK are operated almost exclusively on SP95 ie Unleaded 95.
Most, including our club and the gliding club have run them for thousands of hours now without problem.
Maybe @aart has a point as most of our engines are not the most recent models.
Asking an AI bot for the average height of light aircraft airfields in Switzerland:
“The average height above sea level of Swiss airfields for light aircraft is 1,533 meters (5,031 feet)”
( but I wouldn’t trust that figure). But could possibly be a factor?
A whole bunch of engines, with a whole bunch of fuel related issues. It’s difficult to draw any conclusion from that, other than it’s important that the engine gets fuel in the right amount 
That isn’t exactly news.
2greens1red wrote:
( but I wouldn’t trust that figure)
You shouldn’t. It’s a bunch of c**p. AI is not a reliable source of data. It makes up nice stories, but is a good example of garbage in, garbage out.
Samedan LSZS claims to be the “highest airport in Europe” and it’s 5’600ft. Just as a guess, I would say the average altitude for airfields in Switzerlands is somewhere in the range of 1’500-2’000ft, perhaps even lower. If anything, density altitude could be a factor. But I suspect that most of these incidents weren’t on 30°+ days.
The German LBA is now also jumped on the bandwagon. See here.
A recent SB for the Bristell B23:
