When I tried to flash and install the SuperSU latest zip on "Aosp extended Oreo ROM for Moto G Falcon model it is not working. Adding a screenshot also below. Magisk is NOT installed.
I get that error even with systemless on various ROMs. The fact that AEX booted with system mode means you're good on that point.
On other phone running Dirty Unicorns Nougat I kept getting that even after reflashing SU a couple of times. I then flashed 2.79 and updated via the Play Store.
Anyway, when that error dialog pops up you have the option to see possible fixes. One suggestion was to go into SU's settings and choose the cleanup for reinstallation from Play Store option. On one ROM I did that and just reflashed SU. It worked.
On DU it didn't so that's why I went down to 2.79 first. Not sure if 2.79 will work on Oreo.
I tried system mode SU on an early Tesla O build where it worked the first time.
I guess it's time to start playing with the O stuff again.
LG G3 D851, PAC-MAN LP ROM, MultiROM, Tapatalk 4.9.5