Not really, no. I did not think I did anyhting special to cause it.

I had just the browser and email open, I was reading TMO on the browser when something happened and the device froze first, then booted.

When it started booting up, it went to fast-cycle reboot loop, the "Jolla" text came in for maybe 2...3 seconds, then it went dark for 2...3 seconds and so on. No reaction to power button, and when I removed the battery it went straight on to same cycling after I inserted it.

To cure it, I connected it to my PC, pressed vol-down and inserted battery. When it detected the USB connection it created the IP address 10.42.66.80 on the linux box. I tried telnetting to 10.42.66.66 as adviced, but it as not reachable.
After that I manually gave the linux end the IP address 192.168.2.14 and managed to telnet to the device at 192.168.2.15.

After giving my security code as password, I got the menu and used the option 5 to break the looping.