Guide: split-Protonmail (offline send/receive qubes + pm bridge vm)

WaitForSession error?

I’ve fully implemented the protonmail-bridge and mail-receive qubes, but when I try to check mail in Thunderbird nothing happens. journalctl in the mail-receive qube shows the following error:

host qubes.WaitForSession-dom0[2238]: Cannot access user instance remotely.

while all seems good from dom0, which only shows:

dom0 qrexec-policy-daemon[2495]: qrexec: qubes.ConnectTCP+1143: mail-receive → @default: allowed to protonmail-bridge

There was a fix for the WaitForSession error in discussions of the split-browser, but I don’t see how the fix may apply here.

Anyone have ideas on how to proceed?