Hi @hube268,
Can you confirm that the Pixhawk is being detected, and that the versions are in fact the latest stable ones for Companion and ArduSub? You should see all of the following on the System page (http://192.168.2.2:2770/system):
If the ArduSub version can’t be detected then most likely the update was not in fact successful, in which case you may need to connect the Pixhawk to the topside computer directly, and flash it via QGC’s Firmware page.
If it is being detected then our troubleshooting docs may help 
Are you aware that Companion is no longer being developed?
BlueOS (its replacement) is into stable releases now, and we’re in the process of making a proper post about that which recommends switching to it, but that post may not be complete for a few more days (and I figured this is better to flag for you sooner rather than later).