I noticed that the MEDM RED/YELLOW/GREEN field associated with CP4's dewar level had changed today from the nominal RED (CP4 is empty - decommissioned) to YELLOW and 1.3% full up from the nominal ~0% full -> I think that this is a bogus indication and should be ignored.
See attached plot for dewar level, behaviour changes on 12/08/2019 around 22:00 utc, around 14:00 local time.
For now I've adjusted the high alarm level for this channel, from 1.0 to 1.5, field is green now.