User @1n4ts experienced difficulties reported here S9 from stable (oreo) /e/ via Stock Q ROM to /e/ on Q.
I am not quite sure of the exact error to report as a Documentation suggestion but I think two things:
On some devices, installation can fail if vendors are not up-to-date. In this
Patch the device
are required under certain conditions but there is a lack of clarity, in that any user might think they have to follow the guidance.