Since some days the flow designer won't run any more in my Sandboxes. The message tells me to activate or download Adobe Flash Player. Everything works smooth in my Production Org.

I am using Mac OS X with Safari or Chrome. If I start up my Window 10 in Parallels and use Edge or Firefox there, the designer will work as expected. It is just Mac and Sandboxes in combination. Any explanation, maybe something with Locker Service?