Is there a difference in the wiring between the flight controller and the computer in both setups? Are you sending data (mavlink messages) from the computer to the flight controller?
Okay so it happens when the Herelink is connected to the cube via telemetry 2 port, but strange because telemetry is working fine when itās connected, but video does not work, If I unplug telemetry it works every time 
There are many differences but unplugging things one at a time lead me to the telemetry,
the UAS is using CAN GPS here3 and orange cube.
My test bench is using here2 GPS I2C and black cube, I did set the orange cube up along side the black cube, but never thought to test the HDMI part of the herelink as I thought it was independent.
My video steam settings are enabled, just not sure why it works only without telemetry of herelink connected
@philip thoughts?
Okay I figured it out!
Itās a setting called MAV_MODE, it was default set to onboard, instead of normal which when set correctly allows the video stream to work normal.
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Great, I think this might be a very useful information for other users!
@Baptiste.K, could that be related to our problem?
Herelink video stops because of companion computer? - HereLink - Cubepilot
Can you explain more? Where is this setting at?
Does MAV_MODE refer to this enum?
https://mavlink.io/en/messages/common.html#MAV_MODE
I seeā¦I was assuming Ardupilot.
Hi and thanks for the heads up !
I was waiting for more information on this MAV_MODE params, but it seems particular to PX4 if iām not mistakenā¦ Is there an equivalent in arducopter ?
Ok, sorry, I did too.
As far as I understand it this setting defines the set of messages and rates send via mavlink on the specific port (which is the port connected to the computer I guess?).
We need now to look into the differences in messages between the two settings.
Lolā¦ PX4ā¦ ahā¦ 
So does this imply that turning the MAVLINK_MODE_1 setting off will fix the hdmi issue?
I would say it is possible that the messages which are send when having activated the mode are connected to at least one of the HDMI issues.