ShoreTel / SpeedFusion Inquiry

Does anyone have any expertise with getting ShoreTel to work between multiple sites using SpeedFusion? We did a test yesterday and the networks could all reach each other but the ShoreTel switch to switch connectivity was flakey at best. I think it had to do with us not cutting over all sites. The other PBX switches were on our MPLS that routed to our 2 test sites via the data center and SpeedFusion - internet connected circuits. Maybe too much lag? I wanted to see if anyone in the community has already accomplished this and could share some wisdom before we cut over of all sites. We did reach out to ShoreTel and they do not officially support any 3rd party WAN Aggregation/SD-WAN/etc. devices. They never said it wouldn’t work, just not supported. Thanks ahead of time!

Can you share the graphical network diagram for better understanding?