Issues connecting to secondary network OPNsense instance

[skybolt_1]

I have two networks at two different physical locations. The first network is address space 192.168.9.0/24, the second network is 192.168.19.0/24. Both networks are managed by OPNsense gateways. The networks are connected by an IPSEC site-to-site VPN, 256 bit AES-GCM with 128 bit ICV + SHA256 + DH Group 16, Mutual PSK authentication.

Ever since I set this system up, I have had an issue connecting to the https://192.168.19.1 gateway address of the remote OPNsense instance from the 192.168.9.0/24 network. I am able to navigate to the login page, it throws an untrusted certificate error (have not replaced the self-gen certificate). However, the page will either A: never load or B: load after waiting about five minutes but without the bulk of the graphics. See the attached screenshots.

More concerningly, if I log into the OPNsense instance at that strange looking login screen, it is a tossup whether the OPNsense instance will crash in some way and require a reboot.

These issues have persisted all the way back to when I was using pfSense.

Has anyone seen issues like this previously?