I contacted Flightradar24. They say they checked their logs several times for the time spans in question and did not find any abnormalities.
As far as we can see no aircraft has disappeared from our system. Also the more advanced and more sensitive MLAT system (4 receivers needed to track a flight) was working during this time.
With about 30 receivers in the area between Vienna, Munich, Karlsruhe, Praha and Bratislava Flightradar24 has probably more receivers than ATC and therefore a bigger redundancy.
We are not saying that there was no interference during these time periods, but if there was some kind of interference it looks like it didn't affect our system.