Previously, the device was bootlooping.
However, I could, and still can, get to TWRP and I think I may have attempted a restore, or a wipe.

Now it starts to boot, and I get the error message listed in the title of this post.

Before the bootloop issue, I was on an official MM ROM.
MM had been bugging me for a little while that there was an OTA update.
I'd heard that I couldn't do the OTA on a rooted device and didn't want to bother with uninstalling SuperSU and TWRP and then rerooting after (not at that moment), so I long-tapped on the notification an told it to stop notifying me.
The next day, bootloop.
I wonder if it installed the OTA.

If this were a device with an SD slot, I'd just find a ROM and flash it from there with TWRP.

TWRP is still on the device and I can still access it.
I don't know how I can get any information about what's installed, or if there are error logs.

Any suggestions on what I might do without having to flash?

Alternatively, if I do have to flash, should I continue with the OEM/carrier ROM? (It's a Wind Mobile device, being used in Canada, but not on Wind.)
And any advice you might think would be good or me before getting into this?