Looks like it has only the sysupgrade image (as also the OEM firmware is based on OpenWrt), but it also needs specific flashing process to reset settings. Read from the commit adding support for Comfast E110N
No experience with the device, but the core of that commit message is that the OEM firmware settings may survive, as the original firmware is an OpenWrt variant.
Resetting the router via button, from LuCI menu or with "firstboot" on console should be enough.
Unfortunately, this was not the solution. I had taken the firmware and implemented it. However, I didn't get any errors or anything like that, but the modem stopped responding and got into a BootLoop. Because of this I had to start a TFTP connection again and put the OEM version of Comfast on it. (For the people who have the same problem, the modem loops on 192.168.1.1 ask for file "firmware_auto.bin". But implement it on ip 192.168.1.10 this seemed to work for me, I had to try couple of times but after a while he took the image and rebooted back.)
Then I went back and found out that everything worked when I was running on version 18.06.2. However, not version CF-E110n but CF-E320N uploaded it and I immediately received the OpenWRT back.
So this topic is solved and I hope to have helped several people with this in the future.