The issue on setup of these devices is related to this. As far as I can see, this is unlikely to be the real problem, as defects in band-steering algorithms would wreak serious havoc on a huge variety of 2.4GHz-only client devices. Some attribute the problem to band-steering in routers, which is a murky non-standard protocol that routers use to 'encourage' devices to switch bands by selectively ignoring packets on one band or another. Below is an attempt to deeply explain what the problem is.

These troubles are running rampant, and from what I can gather, have an intricate and subtle cause. Since you're asking, you may have come upon these concerns because you've heard about trouble configuring IOT devices when you have dual-band WIFI. Until people want to pay extra for an IOT chip that's dual-band or 5MHz only, that's what you'll see on the market.

Most of these IOTs only connect to the 2.4GHz WIFI band because that's what the cheapest WIFI+microprocessor chips: mostly ESP8266 chips, are able to do. It's the routers and access points that will complete the connection to 5 GHz band devices. The bulb itself will only connect to the 2.4GHz WIFI bands directly. It can even happen with two separate routers, each on separate LANs, so long as there is a physical connection between them and routing paths configured to connect one LAN to another. It can also happen with two separate routers or access points, so long as each are connected to a common LAN. This will happen (most common case) if you have a router with both 2.4GHz and 5GHz band wireless, both turned on, even with different SSIDs, with DHCP service on, or with the two devices assigned to addresses on a common local IP network. A device on a 5GHz WIFI band and a device on a 2.4GHz WIFI band can pass TCP/IP packets to each other (connect) if each band is associated with a common local IP network.

Instaling LightBulb 2.4.6