@OnePlus6user hey, I tried to perform next OTA update with Lineage recovery and unlocked bootloader and it didn’t work too, I had to flash TWRP and do the update manualy (with zip file), then it booted correctly without loosing any data.
I’m not sure about the startup message with locket bootloader, I don’t remember to be honest 
I can still try to lock bootloader and check it, I could re-unlock again afterwards.