I'm experiencing this today (July 16, 2020), and it's extremely frustrating - especially as I'm experiencing it while trying to record a tutorial video to demo the operation of the Arduino IoT Cloud!
I have the world's simplest demo, an LED connected to a Nano 33 IoT board. On the web dashboard, I can control it perfectly with both a switch and a pushbutton.
But both the switch and pushbutton on the mobile app have the same error described by @blueeyedpop.
I have rebuilt this from scratch two times now, using different variable and dashboard names, and the same results. I have also built it with just the switch and just the pushbutton - same results.
Have restarted my Android phone (Google Pixel 4a) and have even reinstalled the mobile app - still won't work.
Not sure if it's relevant, but I'm on the Maker plan.
Any help would be appreciated. Thank you!