Hi,
Can you please specify your setup more in detail? I‘m afraid, that there are several restrictions to any object referenced within XRef Scene(s) and as far as I know, there's currently no way how to bypass this limitation, therefore the recommendable workflow would be to use XRef Object(s) for used Custom Object(s) and insert FP objects in the "master scene".
Thanks in advance for any further comments on this issue you can share about it with us / our user community (in case some user(s) will run into similar troubles).
Best regards,