@majorz
Thanks again for your help with this.
I followed the steps you outlined above, with some interesting results.
When setting the wifi credentials with nmcli d wifi connect SSID password PASSWORD, I encountered a timeout several times. I then attempted to connect to a different Wifi network, and it succeeded.
root@8098331:~# nmcli d wifi connect SSID1 password PASSWORD
Error: Timeout 90 sec expired.
root@8098331:~# nmcli d wifi connect SSID2 password PASSWORD
Device 'wlan0' successfully activated with 'xxxxx'.
After seeing wlan0 successfully activated, I continued with the steps you outlined, and the issue did NOT replicate; on rebooting without the Ethernet cable attached, the device did connect to the wifi network (SSID2).
However, connecting to the original network (SSID1) did work on the previous ResinOS (version 2.12.7). So this seems to be related to the combination of network and ResinOS version. (As a side note, I am working with Raspberry Pi 3 B+, so both 5G and 2G networks should be compatible).
I have enabled support access, and will PM you a link.
Thanks again!