I came in and found the PSL had tripped about 6 hours ago. It is again correlated with some flipping of the diode chiller flow monitor bit. After the trip, the bit flips for about 40 s before returning to the OK (1) state.

When I went to reset it, both chillers were on. The diode chiller has been holding steady at 20.5 lpm or so for the past hour (not sure about further back in time).