The grey flags were denoting missing channels from the LaserAmp processes.
Following the procedure in WikiOperators, I found that the relevant servers (ServerMbAdsMB on Olwin and LaserAmp/EER on Astor) were both off. So at around 00:40 LT I started these servers and then performed a reload of FbsAlp collect process. After these actions the channels were again available and the DMS flags back to green (see attached plot).
As can be noted from the plot, it is worth to mention that before the period of data missing (stared around 18:30LT), the data were flat starting from around 10:00 LT. This is even worse, because it is misleading for the DMS: indeed they remained flat at a value within the DMS tresholds, that therefore remained green till the above said event of data missing.