You might want to contact our support team. We have deliverability experts on the Support Team, and if they can't help, they can escalate you to the Privacy Team. There are a lot of reasons your deliverability can change when you switch providers, anything from needing to establish a new reputation to having issues with data migration. Similarly, not every provider measures things exactly the same, so sometimes the numbers look different because they're actually measuring different things. Support is a good place to start to try to determine exactly what factors are at play for you.