I had a U22 that did the same thing with CE installed to the eMMC only my ethernet port completely ceased to function with CE & I still used DHCP. (CE updated from 18 to 19 & I did a hard reset of CE, it wasn't immediate but it was very soon after this CE update & reset that the ethernet port then apparently failed & no longer registered a MAC address at all.)
After extensive troubleshooting, re-flashing the MINIX firmware back to the eMMC & physically dismantling the affected U22, the ethernet port then began to work again but somehow the original MAC address had been completely wiped & replaced with the date of the Android firmware build itself.
I continued to use the device for a while with both the official FW & CE running from an SD card but soon afterwards the ethernet port permanently ceased to function. Since, I've tried various means to rectify the problem but it appears to now be permanent.
I've also tried installing FW with root & attempted to reprogram the MAC address back to the original address but nothing has worked so far & the affected U22 will now only work with WiFi which still has its original MAC address. (Obviously, because your device no longer has a recognisable MAC address you can't reserve an IP from your router & it may interfere with other normal network functions.)
I've never experienced this with any other network capable device before & there is definitely a direct correlation with installing CE to the eMMC & allowing it to update and/or reset. Unless absolutely necessary, I'd strongly advise against installing CE to the eMMC as so far I've been unable to reproduce this issue with 2 x additional U22's running Android from the eMMC & CE from SD cards. (I'm not going to attempt to recreate it again with CE installed to the eMMC for obvious reasons as I'm now reasonably certain I could recreate it & that would potentially be another U22 with a dead ethernet port!!)
Ideally, both MINIX & CE's devs need to test for this issue themselves as it essentially renders an ethernet port dead or very limited at best.