After reading the advice given so far, if I were the original poster, I would be changing the account to a Business account straightaway.

With around 7,600 listings, I would not want eBay taking a closer look and deciding the account is being operated as a business while still labelled as private.

It may not be the reason for this particular warning, but it is a risk sitting there in plain sight. If eBay lowered the selling limits, restricted the account, or removed a large batch of listings, the damage could be far worse than simply changing the account type now.

Relisting 7,600 items from scratch would be a nightmare. That is not a weekend job, or even a one-week job for most people.

If the selling activity is effectively business selling, then the account needs to reflect that. I would rather deal with that now than wait for eBay to decide the matter for me.