I'm getting the same issue. It works with Freshsales, but HubSpot gives an authentication error. There is no option to use TLS in HubSpot, which Apple requires. In Freshsales, this is possible. Perhaps this is why? I'm evaluating this for a client, and right now, HubSpot would have to be discounted on this basis.
I've checked internally to see if there have been similar reports, but I wasn't able to find any cases where the missing TLS option would prevent users from connecting their email with HubSpot.