I also had this problem recently. As the main account holder, I could not share data from abroad, and neither could my family member in the UK. Had to cancel my EE SIM, and ask for a new SIM to be sent to my UK address at which point my family member was able to share my data.
EE customer service said once the main account SIM leaves the UK network, data sharing cannot be done. I think it is an unreasonable restriction, maybe if enough complain they'll remove the restriction.
