I don't know if this is where you track it, but the problem described here appears to have made it into Ubuntu Advantage 16.04-ESM as well, specifically across the 4.15.0-189.200~16.04.1 -> 4.15.0-193.204~16.04.1 upgrade. (Just based on changelog text this fix was not in 4.15.0-194.205~16.04.1 but I haven't dug far enough to track more closely.)
I don't know if this is where you track it, but the problem described here appears to have made it into Ubuntu Advantage 16.04-ESM as well, specifically across the 4.15.0- 189.200~ 16.04.1 -> 4.15.0- 193.204~ 16.04.1 upgrade. (Just based on changelog text this fix was not in 4.15.0- 194.205~ 16.04.1 but I haven't dug far enough to track more closely.)