DIAGNOSIS You have "Power-on behavior" set to the default, and a brief power flicker (like from your utility) is restoring them to 'on.'
FIX Change the default power-on state for each bulb to 'Last used state' or 'Off.'
- In the Hue app, go to Settings > Lights.
- Select a bulb, then tap "Power-on behavior."
- Select "Power loss recovery" and choose "Last used state."
- Repeat for every bulb causing the issue.
IF THAT DIDN'T WORK Check for any automated routines (Home & Away, other apps like Google Home) or third-party services (IFTTT) that might be triggering them. Disable all and see if it stops.
HEADS UP If you set the behavior to 'Off' and have a real power outage, you'll need to turn the physical switch off/on to get the bulb responsive in the app again.