Hi, I have exactly the same problem:
I have installed /e/OS following the official guide.
When at the end of the process I type fastboot flashing lock_critical, the phone reboots, I get a warning that the bootloader is still unlocked, but the phone eventually boots in /e/OS.
Next, when I type fastboot flashing lock, the phone reboots and I get the warning that ‘The device is corrupted’. It enters into a bootloader loop. No way of booting in /e/OS anymore.
I have tried with both IMG-e-0.22-r-20220224165878-stable-FP4.zip and IMG-e-0.21-r-20220112156786-stable-FP4.zip but it did not make any difference.
I have tried the solution proposed by @chrisrg but it did not make a difference.
The result is that I am currently using /e/OS but the phone is still unlocked and I get a warning every time I restart my phone. How to solve this without going through the entire installation again?