Connections in dual port 4gb FC HBA's

We recently had an issue with our M4000 server when our SAN Administrator did some switch upgrades/maintenance  on one of switches but the server lost connection to both HBA cards despite the fact that one of the switches was still available, which caused the non-global zones located on the SAN to lock up.

When we checked the connections from the HBA cards from the back of the M4000 there are 2 dual port 4gb FC HBA's, but here is only one cable in each HBA card. (2 cables in total instead of 4).

Should there be 2 cables in both ports on both cards to ensure we have the resilience to the SAN and could this be causing the issue with the loss of connection to both HBA's?