Thanks for the replies guysYeah, your cassette should freewheel and chain no move when no pedalling. The shimano motor also has a freewheel in it so the chain wont move when you pedal back. Sounds like the resistance in the wheel freehub is higher than the motor freewheel, which it should not be.
If the rear wheel has been apart it may be an internal spacer has been lost or the hub mis-assembled. Try to move the freewheel on the bike, then remove the wheel and see if its better, might help you/us diagnose the issue.
However an email to CRC is the first thing you should do, hopefully they will need just the wheel and not the whole bike for a repair.
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