Email forwarding problem

I just started using Polarismail and I'm having a huge problem with receiving forwarded email.

I have a mailbox setup to forward email to an outlook.com email address, but it does not forward reliably. There are many emails in the mailbox at Polaris that are not reaching Outlook - not in spam or anywhere. And there are no undeliverable emails bouncing back to Polaris. Outlook is either silently blocking them or they are not being forwarded at all.

Anyone have that sort of experience with Polaris or any other email host? Anyone know why that might be happening?

And it's inconsistent, I was trying to get a 2FA code from a website and the first two times it didn't reach Outlook. The third try reached Outlook, but all three were sitting in the mailbox at Polaris.