[Elecraft] KPA500: strange behaviour - any ideas?

[WM3M]

KPA500 and K3 set up does this also.
I have tried to duplicate it without much success, it is somewhat random.
What I think the cause is, the output power of the K3 exceeds what the
KPA500 wants, even though I have set it per band, I think sometimes there is
a spike in power, causing the KPA500 to fault.
This is a guess on my part, since if I cut back on the power on the K3 it
does not do it as much.
The other thing I have noticed,  it does it more on certain antennas, so it
could be related to SWR.
I have the KAT500 too and SWR is checked before I transmit with the KPA500.
I tend to transmit on the same freqs a lot.  Some days it will work
flawlessly, then the next day, with nothing changed, the KPA500 will have
this problem.
Please advise if anyone figures this one out.   Thanks
Emory  WM3M