Someone can correct me if I am wrong, but Hubitat cannot block a particular device from pairing.
On the other hand, a device might not be compatible for whatever reason. One famous example is the old Iris V1 that are incompatible with the Zigbee chipset in the C8. They are incapable of pairing with a C8.
To some extent, Aqara and even some Tuya suffer from being not exactly following Zigbee standards, but those often manifest the issues in a different way, like the Aqara pairing but not staying paired. I seem to recall Tuya show as attempting to pair but will time out or never complete the pairing.
For one device to not pair, yet other completely different items pair without issues in my mind points to a particular device that is for some reason incompatible. I will concede that it would be unusual to get 3 sets of bad bulbs, but if these were all from the same batch, or all were counterfeit, or all were of a bad firmware, I could see how they all sets of these might not work.
You know that for a fact, or are assuming that? They are selling an item, they should stand behind it somehow?
That is an interesting question. But depends upon the next question.
Possibly, but hard to tell. Again Sengled support would be the one to ask if there have been any recent firmware updates, or any at all.
So you could buy their hub and theoretically do an update. That is an added expense, although not too bad ($30 or so?) but there is no proof an update exists, or whether it would help. A 3rd party hub for the most part isn't going to "play nice with Hubitat". You can't join a Zigbee hub to another Zigbee hub, there can only be one "master" controller in a network.
Maybe they put a Wifi chipset in these bulbs instead of Zigbee, what then? I guess you might know that they don't pair with the Sengled hub, but not why it fails.
On the other hand, if they do pair with an alternative hub (other than Hubitat) I guess you could point to an incompatibility somewhere. But it still doesn't prove the hub is bad, or why. Other people seem to have paired these, so again it is evidence the hub and bulbs are capable of joining (or were at one point).
This is probably what I would try as the easiest and quickest to get around this.
I believe these are the same manufacturer as Orein? Probably others as well (Linkind?). I have used that Orein brand (A19 bulbs though) and haven't had any issues with them. I think they all use the Aidot app.
www.amazon.com/OREiN-Control-Reliable-Changing-SmartThings/dp/B0CNVXJ4SK