Though I’ve no personal experience with this card, Sangoma has excellent troubleshooting tools.
The info at Sangoma Documentation should let you determine where the trouble lies.
Is FreeSwitch (Fusion) to Asterisk (FreePBX) SIP Trunk Connection still relevant?
If so, it should not be hard to determine the cause of lost registration, fix it and connect directly by SIP… That would give you multiple channels, better voice quality and many other benefits. Who is the provider?