Total rubbish, the only hard limit is the number of IP addresses the hub can allocate. Not sure what the DHCP range of the hub 3 is, but it is certainly a lot more than 9!!
For all intents and purposes you will not be able to exhaust the number of devices that can connect to the Homehub. I seem to recall reading somewhere that most routers can handle about 250 devices connected by wireless although this would obviously put a strain on your network if they were all downloading at the same time.
If your devices are dropping out, is it only wireless or is the wired connection also dropping.
If it is only wireless it could be interference that is causing the problem. If it is both wired and wireless it could be your Internet connection that is the problem.
The first thing to try is a factory reset of the Homehub by pressing a pin into the recess button on the rear for about 20 seconds. This can often sort out problems.
If that doesn't help, post back and include what type of broadband you have, ie Infinity or "normal" broadband.
We've fairly often had around 15 devices connected at once with no problems. The HH3 would probably struggle if they were all working hard at the same time and talking a lot to each other as well as to the internet.
If you're having HH3 wifi problem join the long list of people here https://community.bt.com/t5/Other-Broadband-Discussions/HH3-Infinity-Local-WiFi-Channel-fade/td-p/14...
There is a fix the mods can apply so go post a message. This is a far wider problem than just these forum members I'm sure, but the helpline doesn't know about it