Hi,
On the software side, first yes this is old software, TCNC6.2 was released in June 2014. The latest on the TC train is TCNC7.3.21, released March 2020. The SX20 supports the newer CE software also so you could also migrate to CENC9.13.
If you could upgrade to TCNC6.3 I believe the release key requirement has been removed, the problem is that this deferred software due to its age so it is not available for download. Do you have access to Cisco.com for software downloads?
Another thing to point out is that this device is a non-crypto unit, as stated by the 'NC' portion of the software build, it is more common to have a crypto device, but perhaps you are in a market that forbids them?
As to the issue itself, I'm not clear on what the symptom is exactly, as it seems you are saying video does go to the conference and can be seen in the grid layout by anyone, but then it does not appear in other circumstances. If you elaborate on what steps are taken to cause the issue we may be able to help further, but I would say the first priority is to run the device on recent software.