If you’re not able to arm but have a working MAVLink connection then I suggest having a look at the 'Arming Checks` section of the Safety page. Likely there’s a check there that’s enabled and failing.
That could be a check that doesn’t actually matter to your operation (e.g. GPS lock if you don’t have a GPS, in which case you should disable that check), or it could be something set up incorrectly (e.g. Board Voltage or Battery Level if the power sense module isn’t correctly configured in the Power page), or something else.
If it’s not an arming check issue, please specify
operating system
QGC version
ArduSub version
Companion version
if the same vehicle setup works with another topside setup, which operating system and QGC were used (if they’re different)
Our video troubleshooting steps may be relevant. If they don’t help, which operating system and QGC version are you using?
The system was tested on a different topside setup - arming and disarming and the video feed worked.
It was connected back to the new topside setup and everything worked.
I’m not sure how it got fixed, but the problem has been resolved.
Always frustrating to not know why something is working when it wasn’t previously, although perhaps in this case it just needed a reboot or something to reset some internal state (not sure whether that was something you’d tried in initial testing).