@tridge - We have been struggling with slow telemetry from our second ground station. This was mission planner through Telem 2 with RFD900X connection as a backup to our primary hand controller telemetry.
We would have a fast hook up on the ground but as soon as we switched on our second controllers telemetry, QGrondcontrol through Telem1 it would slow down the telemetry significantly to almost freezing or updating every couple of seconds on the Mission Planner RFD 900 station only. The hand controller telem would be fine and super fast, but only the second telem would slow.
Another interesting thing is when the second telem slowed we would get some items like the Artificial Horrizon and the Ch6 output that would never update.
We were tearing our hair out! We were on the phone for hours to RFDesign who were amazing in their support but couldn’t point it to a connection error as we had solid RemRSSI and RSSI connection.
Finally I called @Leonardthall who has been helping us with our build and he said he had a wild hunch which ended up being bang on.
He suggested turning off the Rx DMA and TxDMA in serial settings for Serial 1, then if that didn’t work to turn them back on on serial 1 and turn them off on Serial 2.
As soon as we turned them off on Serial 2 only we had rock solid dual telemetry with no slow down. I thought I would put this out there for anyone in the future that is having issues with dual telemetry conflicts or slow downs.