Help, can't send items to fulfilment center 'dangerous goods' items being reclassified, what is going on?!

We're quite new to Amazon and using FBA to sell our products - the products are healthcare and although they have safety warnings they weren't considered hazardous. As the manufacturer we're audited by the government so we carry full safety data sheets, which I have submitted to Amazon. We've enrolled in the dangerous goods program and received the below classification (as per screenshot)

But whenever we now try to replenish stock of the ASIN highlighted in the picture we get an error message which reads:

The first part of that error is odd because the shippers are totally fine for dimensions and weight and have been previously accepted. We also don't use Amazon partnered couriers - we use DPD as we hold an account with them.

The second issue seems to always pop up as soon as we click the accept and continue to print labels.

I contacted support who then told me that the ASIN had been reclassified as hazardous - odd, we make it, literally from scratch in the UK and it definitely isn't. but either way, we're still enrolled in the dangerous goods scheme and we still can't ship.

What is causing this error and why is Amazon support so useless? They basically gave us a link back to the hazardous goods page.

I've seen a few conflicting forum posts on this topic, some reporting similar problems, others saying it's not a problem but nobody stating how it can be resolved.

Thanks