Federation: /rooms/.../members fails for the invites received from a federated server

[matrixbot]

This issue has been migrated from #4985.

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Description
get /_matrix/client/r0/rooms/{roomId}/members on an invite received from another federated server fails with the following error:

errcode = "M_NOT_FOUND";
error = "Can't find event for token Token(room_key=u'xxx', presence_key=u'xxx', typing_key=u'x', receipt_key=u'xxx', account_data_key=u'xxx', push_rules_key=u'xx', to_device_key=u'xxx', device_list_key=u'xxx', groups_key=u'xx')";

Steps to reproduce
Consider 2 users userA and userB, created on 2 different Homeservers.
userA creates a room and invites userB
When userB requests for the members of this room, he gets an error