So make sure we are on the same page, here is what I gathered so far: you said sometimes upon reboot the controller bypasses wired Ethernet and goes into WiFi mode, correct? I recommended you to NOT use static IP, but instead, leave the controller in DHCP and use your router’s DHCP reservation to reserve a fixed IP. Is that the case with your controller at the moment? Also, I am curious: if the wired connection succeeds at some point, why do you need to reboot the controller? It sounds like you need to reboot the controller several times but I don’t know why.
There is no point forcing the controller in wired Ethernet mode: if the auto-detection fails, that means something is wrong with the wired connection (either there is a physical connection problem, or the controller failed to obtain a valid IP address from your router). So if we force the controller to be in wired Ethernet mode, it just won’t be accessible. For that reason, the firmware always goes into WiFi mode if the Ethernet initialization fails.
It’s possible that the Ethernet module may have a problem and should be replaced. You can either send a support ticket to arrange for a replacement, or just search for ‘ENC28J60 module’ on amazon or aliexpress.com. Look for the ones with 2×5 pins. It’s a very common module that’s widely available.