You might just be victims of circumstances. The field for 2.07GeV/c is right on the border for the C NMR probe. It looks like when the NMR loses lock it switches to the C probe to start a search. It fails, but does not seem to switch to the B probe. The field is near the middle of the B probe, which locks in real quick. If it loses lock for some reason, try to make sure it stays on the B probe and that is is actually searching (the DAC readback should be increasing and decreasing as it searches for a NMR signal). FYI probe# A probe type 3 field range .17T -> .52T probe# B probe type 4 field range .35T -> 1.0T probe# C probe type 5 field range .70T -> 2.1T