Why can I still not receive OTA updates after flashing stock firmware on my Moto G7?

Question

After purchasing a Motorola Moto G7, I rooted it using TWRP and Magisk. After a few months of having it rooted, I decided to undo the process in order to restore the ability to receive OTA updates. I flashed official firmware and re-locked the bootloader, but I still get the boot warning saying that a separate OS was loaded and that it's a security risk (yellow). After checking the system Settings, I discovered that I still couldn't receive updates either.

Relevant Information

• Product/Variant: river XT1962-1 64GB PVT

• Firmware/OS: RIVER_RETAIL_9.0_PPOS29.114-134-7_cid50_subsidy-DEFAULT_regulatory-DEFAULT_CFC.xml.zip

• Followed this process to restore stock firmware: manually update G7 using fastboot | Moto G7

I'm not sure if this makes any kind of a difference, but I did encounter an issue when locking the bootloader:

root@ThinkCentre-M900z:/home/user# fastboot oem lock
...
(bootloader) Flash valid Android images now
(bootloader) Then re-run this command to lock
OKAY [  0.003s]
finished. total time: 0.003s

After the above command failed to re-lock the device, I tried using fastboot flashing lock and that seemed to work.

root@ThinkCentre-M900z:/home/user# fastboot flashing lock
...
(bootloader) Phone is locked. Rebooting phone.
OKAY [  0.004s]
finished. total time: 0.004s

When I run fastboot oem lock after having used flashing lock, it gives a message stating that the bootloader is already locked.

I have two theories so far:

1. The firmware I flashed is incorrect

2. The bootloader is not actually locked (this seems improbable)

Is there any way to fix this? Or am I doomed to manually installing OTAs until I get a new phone? Please let me know if I left out any important information.

Any help is appreciated.