Bridging VLANs like that is generally not recommended.
How many internal interfaces do you need configured like that?
If it's just one you could try breaking the ix2-3 lagg and reconfiguring the switch to connect Eth8 to ix2 directly and bridge that. Removing the VLAN will probably prevent the loss there.
Make sure you have some access to the firewall other than via the switched ports if you try that as it's very easy to get locked out!
Do you need to filter traffic across the bridge? If not you would be better off using an external switch to set that up.
Hey @Derelict Thanks for the ideas. I've managed to find the issue, and it was an equipment problem on our ISP side.
I ran some packet captures on both the internal VoIP VLAN, and the external SBC interface(our phone comes in over the same fiber asour IP, but on a separate interface on the demarcation unit(T-340)), found a lot of dropped packets, moved onto our WAN switch, and saw that there was an EXCESSIVE amount of Tx/Rx errors and collisions on the demarcation interface. When I dug into the interface itself, found that it was only negotiating at half-duplex, which would explain the issues. When I went back through my old config files for the SG-8860, I found that I had to force it into full-duplex mode as the T-340 for some reason will not auto-negotiate to full-duplex, but if I force my side to full, it works just fine, and not a single error since.