After doing a little research, I suspect that it's possible the complainant is not a customer, and eBay are very unlikely to divulge the kind of information that will let you know the full and/or true nature of the complaint.
However, I wonder if you are aware of the following TOS on A's UK site:
Subject to your compliance with these Conditions of Use and applicable Service Terms and your payment of any applicable fees, A**** or its content providers grant you a limited, non-exclusive, non-transferable, non-sublicensable licence to access and make personal and non-commercial use of the A**** Services.
Effectively, A**** do not want to be used as a dropshipping service, and while a lot of people do it (seemingly) without repercussion, others have had their accounts banned for suspect activity.
I don't know if your customers are receiving invoices with their products, but if so, that is also effectively advertising one of eBay's major competitors with every sale, which may have had something to do with the current situation.
I know that doesn't offer you anything constructive, I wish I could, but it could be at least part of the reason this has happened.
