So, we were playing with a Nokia 2. Did the bootloader unlock, and boom the device would only go to a black screen and PC can only recognize it as Quclomm USB Diagnostics 900E mode. The device can only be restarted to briefly access fastboot after which it will try to boot and get to the same state. The Nokia 2 was on Oreo and August update.
We decided to try the Nougat firmware, and all was working well till the Oreo update was installed and then updated to July 2019. The device, once again, only went to 900E mode. We locked down the bootloader, and it booted normally.
So, quite evident at this point that the bootloader shipped with July and August Oreo release breaks the boot chain if the bootloader is unlocked. I am not sure if that is a bug or done willingly. We did briefly flash the old bootloader and device worked on August update, but RIL didn't load and SIM cards weren't getting detected.
If somebody is unlocking the bootloader, then keep the above in mind. We ended up sticking to Oreo + June update and doing no further updates.