The flows were disabled on homey startup after the update installed. I re-enabled them and it works fine (as it did for 1,5 years since I build them).
These flows all start on a date-time card each minute or each 2 minutes.
I can see the calculations in a flow execute within a second (better logic records the last change time stamp of a variable).
I can also see that different one minute flows start after each other with one second in between.
Nothing that looks like 10x a second…
I guess that Homey allows the flows to run, this is a glitch of the update or restart process.