I've got multiple Hue White bulbs, multiple Dimmer switches and a second generation Hue hub. Sometimes, pressing a dimmer button doesn't result in the bulb reacting in any way. Sometimes I have to press multiple times to switch the light on or off. Sometimes I even have to use the hard switch to get what I need. All 5 dimmers in my house have already (<1 year) exhibited this behaviour at least a couple of times. Some are worse than others.
I think I've never seen my lights ignoring the Hue app.
I wonder what the reason could be and what troubleshooting I could do. All distances are very reasonable (max distance between 2 nearest bulbs is <5 m). Usually the system works. Sometimes the devices that fail in this way are actually those located the closest to the hub.
I would also like to know if the dimmer is actually connected to the bulb directly or via the hub.