I have reported this same problem to Meraki support a few weeks ago. No progress and I am not expecting one. It is not easy for them to troubleshooting, but it makes no sense that this many users are reporting it.
I am seeing it on all our Meraki networks in deferent GEO location, on different WAN links, using RADIUS/802.1X authentication. RADIUS servers are in the Data Centre. Problem is very intermittent, so not easy to capture. I could see that Meraki AP is not getting RADIUS response when the Wi-Fi starts dropping. I also see affected SSID showing as low signal from the laptop while being away from it 3 meters while all other broadcasted SSID are full signal. Not sure if I need to indicate that we are seeing this on different Meraki models and firmware, updates didn't fix a thing.