This screenshot was taken after about 30 seconds of my pets completely ignoring the Follow command. This behavior seems to occur with any persistent AoE, but especially when the AoE includes CC of some kind. Enemy invisibility or perception debuffs on the pets also seems to trigger this behavior.
I've been gone for a few months, but I've been keeping up with patch notes, and I haven't seen any deliberate changes to pet AI since the wave of fixes i27 initially brought with it. I have also observed, rarely, that the bots will run into melee range, despite having sufficient recharge and endurance to remain at range. This behavior is clearly a recent development, and is a regression to pet behavior prior to the i27 fixes.
I chose not to post this as a bug report right away, because conversations I've had in-game suggest it doesn't seem to be a widespread issue, and I'm unsure how to collect meaningful data for a bug report of this nature to begin with. Mainly, I'm posting here for other MM players to keep an eye on their pets' behaviors to see if we can identify whether it's specific to Bots or if other pet groups are behaving the same way.