Flashing the system again seemed to do the trick.

I followed this guide on xda

https://forum.xda-developers.com/oneplus-6/how-to/rom-stock-fastboot-roms-oneplus-6-t3796665

For some reason, my data wasn't wiped...

Flashing the system again seemed to do the trick.

I followed this guide on xda

https://forum.xda-developers.com/oneplus-6/how-to/rom-stock-fastboot-roms-oneplus-6-t3796665

I just didn't flash the boot partitions, so I was able to keep my systemless root.