We don't have the OPJ28.108 to OPJ28.111-12 OTA available as it was not captured. That's one of the unfortunate risks of using a soak test.
Your options to get unstuck would be:
1) wait for the Oreo fastboot stock ROM to be released. No idea when that will be but that should let you formally update to the stable Oreo build, and hopefully save your data.
2) unlock your bootloader, erasing your data. Then you could either flash Nougat again (risky) and then take the OTA update to the stable builds. Or flash TWRP and use the TWRP flashable.