Large imports (All-in-One WP Migration, WP All Import, and similar) can look like abusive traffic to the firewall and get blocked mid-import.
- Go to Security Ninja → Firewall and disable the firewall.
- Run the import to completion.
- Re-enable the firewall immediately afterward.
- Confirm login and key site features still work.

See also How to use the firewall and Whitelisting services.