Here are two more tests I did this morning

• removed the DAC card from the cymac and the models, and restarted everything: signal jumps are still there
• move the cymac2 from the crackling noise lab to the CRIME lab, ans set it up with all the same hardware I was using with the cymac3: there are no jumps, signals look perfect (see plots at the end)

So in conclusion: the problem is in the cymac3 computer, either software or hardware. I tend to excluse an I/O hardware problem, since I used two different ADCs and removed the DAC, without improving the situation.