Which printer model (looks like one of the various HP Latex if I had to guess) are you running?
Are you using the on-board i1 device or an offline measurement instrument?
I would suggest that you back up in Media Manager to the Calibration screen, and look at the Linearization ink density curves (Measurements tab). I would bet that at least one of the channel ramps is wonky (possibly flat or has significant declines.)
I have found that using the on-board i1 on the Latex 200-series units (L25500 and L26500/Latex 260) tends to require a copious amount of media, takes a long time, crashes frequently, and generates errant readings with some regularity. An offline measurement instrument is much preferred for those reasons. Using the on-board i1 on the 300-series (my experience is primarily with the Latex 360) on the other hand, works outstandingly well for most opaque media types.