Good Evening together,
got my OnePlus 9 Pro today and started immediately to get /e/ OS on running, but run in a strange issue.
After some attempts and a little bit confusion regarding the slot a and b thing, I got the sideload ending with
serving: ‘e-1.1-r-20220629200015-dev-lemonadep.zip’ (~47%) adb: failed to read command: No error
The device itself said:
[ 206.616099] Install completed with status 0.
But when the device reboots, it still loops into fastboot.
Someone got an idea?
So as I couldnt proceed in any way, I got MSM Download Tool running, bootet in EDL Mode
(yes as long as it is not bricked, you can just flash boot into recovery image from fastboot loop and then use
adb reboot edl
which is way easier then trying to pull of the button combination at the right time)
I got back on Stock OS - updated the device to its newest available version and maybe there was my issue.
Newest Version of Stock OS is already on Android 12 - newest available image of /e/ for my device is based on Android 11 if I didn’t get anything wrong.
So is it even possible to Install /e/ OS without downgrading stock OS first?
Could really need some advice here
Thanks!
Sadly not, you need to be on OOS 11.
Presumably the MSM reinstated a version of 11?
There’s probably a couple of ways to proceed. You can downgrade to 11 on device by grabbing appropriate packages from XDA thread which I’ll find in a moment. You will need an apk for system updater app so that you can do local downgrade/upgrades etc (I believe it’s missing in OOS 12)
Or you could msm again back to the OOS 11 build (what version is it btw?) and then do a local update to the latest/last 11 build which is 11.2.10.10
Yes MSM first installed a version of OOS 11 - then the device started doing updates for OOS 11 - but then updated to OOS 12 in that process unfortunately 
MSM.exe stated Version 4.0 but Window Title said 5.4 if I remember it correctly. Have to check that again later when I try to repeat process to do the downgrade and then only updating via local update to 11.2.10.10
Thanks for your help, appreciate it!
When you look at the list of roms for your device on the xda thread you will see that after 11.2.10.10 the remaining roms have a C number,C.47 etc, these are all OOS 12.
Good to know, maybe this information about the Oxygen OS Version should be added to the Install document for the device.
Just downloading rollback package and Local Update APK to try this way of going back to OOS 11.2.10.10
Went back to OSS 11 through the rollback Package and Local Update APK
Then installed OS 11.2.10.10 through local update.
Proceeded with the Install documentation there, worked fine now.
Except that I had to do Flash Recovery + Sideload Image 2 times, once for Site A, once for Site B.
flashboot getvar all
to see which one is selected right now in fastboot
flashboot set_active a
to select Site A for example
If you install the 2nd Site, skip the Copy Partitions Script (at least that was, how I did it)
Now /e/ OS is working fine. Thanks @chrisrg