Hi Mark,
I have uninstalled, re-installed the RJ several times - all to no avail... In response to a support ticket, all that JF Support had to say was:
"When trying to import a flightplan into the FMS, have you populated the "CO ROUTE"
In the co route box, if you enter your route as YBBNYMML, this will import the flight plan."
Manually entering the co route does work but that was not previously required - and is an unnecessary nuisance...
Even with a brand new MSFS 2020 installation (a massive download) and only the RJ installed, the problem persists. I have two copies of the RJ. One from the MS online store, and a .exe install file from Justflight. Both versions react the same.
This is immensely frustrating - so I have relegated the aircraft onto the back burner.