The zip doesn't have support for A/B partition. You have to install through the app. Put it in '/storage/emulated/0/Android/data/de.robv.android.xposed.installer/cache/downloads/framework' then enable 'show outdated versions'.
Place the installer zip in the directory
So the full path including the zip I use for 8.1 on the pixel XL is
And then re-launch the installer app and click on the installer and select "install" and it works!
This is the way to fix it, thank you!
The download within the exposed installer does not appear to work either, so this is the only way to do it currently it seems if recovery install doesn't work for you.