The log suggests that FlytOS was running for about an hour, and within that time frame, it stopped receiving the heartbeat from Solo 4 times. This is definitely an issue, but:
It seems the issue has now shifted to Solo not sending its acknowledgement within the timeout, due to which APIs respond with a failure status.
Is it possible for you to just get Pixhawk + GPS (not a full drone), for your easier testing? Of course, you won’t be able to fly, but you could easily go through with static testing.