I just installed with the latest KDE image, but I'm able to reproduce this with any of the images available.
After going through the initial configuration, wifi works great. I updated apt and upgraded everything. Then I installed the armbian-firmware-full package. After rebooting wifi still works. Then I setup Bluetooth for my mouse and keyboard. They work correctly. After rebooting I no longer see any networks to connect to for wifi. If I disable Bluetooth and reboot wifi works again and so does Bluetooth.
Is this an issue of daemons or drivers loading in the wrong order?