if you still have the packet loss problem on BAS with SNR=12.7dB then all we can say it's not because of low link margin.
The next culprit often is your harddisk especially if used by other apps. Are you sure your HDD is using CMR recording?
What exactly is the model of your HDD? If the problem is on BAS only while HVS-1 has no problem: Do you use different
HDDs or disk partitions for BAS and HVS-1? For CMR versus SMR recording search this list ...
P.S. It's also good practice to check the logs of your TC clients. Something unusual found in there?