I faced the same issue addressed in the ST forum thread linked here: https://community.smartthings.com/t/smart-bulb-randomly-turns-on/93409
I have two tunable white-only Sylvania smart+ bulbs (formally Osram Lightify I think) that would randomly turn on throughout the day, and most problematically, in the middle of the night. I believe this was due to a firmware issue that the manufacturer has not resolved that causes the light to reset (and turn on) when it searches for OTA updates. In my case, disabling OTA and updating the device handler did not help, so I used webcore to design this workaround that doesn’t solve anything, but doesn’t wake us up.
Here’s how it works: Rather than turn on and off the bulb, I created a virtual dimmer switch that when turned on/off or set to a dim percentage, triggers the same action in the smartbulb. When the bulb turns off, it first dims to 1%. When it turns on, it sets the level to whatever the last level of the virtual switch was.
I then created a second piston that whenever the bulb turns on, it checks to see if the virtual switch is also on. If it’s not, the bulb immediately shuts off.
I also created a virtual switch that controls both lights (‘Bedroom’), allowing me to dim the group at once.
How this works in practice: In intended uses, I don’t even notice I’m having Alexa control a virtual switch instead of the bulb directly. Throughout the night, the IDE informs me that the bulb still turns on randomly, however it does so at 1% for less than second, so is unnoticeable. It’s clunky, but fixed my issue in 20 min so works enough for me. Hope this helps someone out