Can you replicate it by tweaking the plug in the KPA output socket?
I had huge problems like this for a long while.
Turns out that the SPDIF output socket on the KPA wasn't a good connection to my cable and even a small movement of my KPA caused it to drop out. Sometimes it happened and sometimes not.
I ended up pulling the back off the KPA and bending the connector so it really grabbed the plug...problem solved.
If your's is under warranty, might think twice about doing this.