Service that report / check IPs for email spam have no value when it comes to Pinterest.
If the proxy is considered "bad" the account is going to be immediately suspended the first time you pin to it (if Pinterest lets you create an account with the IP at all). So it's unlikely that the problem is that the IP has been flagged.
Indeed it is not the case, because the ban comes even after several weeks
Now, if the IPs are too geographically similar (e.g. 184.108.40.206 and 220.127.116.11 and 18.104.22.168 etc)
At first, but after that I changed the provider and the ip were very, very distant each other; nevertheless got several ban
the accounts were created close together or are too similar to each other (same board names, same topics, pinning using the same keywords etc) then Pinterest might tie those accounts together and suspend them all.
I will try to pay more attention to this aspect; after that I don't know..........