Same boat. Triumph shows bosses defeated 9/9. Visions of the travel is 8/8. Motes of light is 16/17. My issue is that Bungie are giving two different explanations. It is either due to Taken Servitor Meatball drop issue OR the Triumph tracked a boss as defeated when I haven't actually defeated it. There are two different solutions that both consume a lot of time. I either grind the hell out of The Blooming hoping I get Taken Servitor Meatball AND that it drops the missing mote OR I grind all Overthrows in the hopes that a boss that I haven't defeated pops up AND drops a mote. The only saving grace is that one of the areas will have matchmaking, as with 2 other competent guardians you can normally do the full overthrow in 10-15 minutes. Otherwise we're solo grinding an area which can take upwards of 25 minutes and is boring, all for the chance that that overthrow MIGHT give you the missing mote.

From what I went through and have seen these are the common factors in missing a mote. The three lucient hive in the landing. Tormentor in the impass. Meatball. After the last immune phase you must kill ALL ads before the boss

Yes this is what bungie told me Thanks for reaching out! If you haven’t acquired all of the Motes of Light yet, make sure you’ve collected and placed all Visions of the Traveler and defeated all Overthrow bosses in each area. If you’re only missing the defeat of the Taken Servitor boss, we suggest you try to eliminate it a couple times, making sure to return to Orbit between attempts. Please note, we’re currently addressing an issue where the triumphs tracking the defeat of Overthrow bosses are not working as intended. Therefore, please don’t rely on these Triumphs as confirmation of your successful defeat of all unique Overthrow bosses.

I'm the same, one mote short and I did these bosses in order to make sure I missed nothing. My guess is the motes are the same as gambits and those are notoriously bad for clipping under scenery. They should have allowed for extra to drop repeating bosses - just in case. No way am I going through that again hoping 'a mote might drop'

I got the 16 motes. All the Vision globes are placed. All three triumphs are done so no other bosses were needed supposedly.I found someone who figured a workaround out. If you put your 16 motes in vault and do all levels of overthrow in Blooming .Meatball spawns.I did it this way and got the Primordial finally but.When i went back to the vault grabbed the motes and went back to chest in Lost city it says "You lack something" So this bug is an issue in more ways than one