<group> is randomly switching on and off my lights

[Peter_Kawa]

From my point of view, when you’re the only one experiencing & reporting this behaviour, the app can’t really be the issue.
It might be an idea for you to replace “frustrating” with “learning curve”

it’s possible you configured the group’s options in a way which acts differently from what you expected.

I’d suggest you start with a three lights test group, and test all options to see what happens, and what doesn’t happen.

I suspect you used/enabled one of the advanced group options:

@Jamie

Advance Groups

Unified Groups
These same as a normal group, but you are no longer restricted by device class.
You can use these groups for additional flexibility, or advance use cases, but the advance settings are harder to manage.

Blended Groups
Group that include devices with different capabilities.
You can use these groups to control similar devices, for example a group with a light which only dims and a light which has colour changing capability.
When changing the the brightness, a blended group will change all devices brightness, but changing the colour will only change that on the devices where it is possible.

Fused Groups
These are a special type, which “fuse” devices together, creating a single device out of one or more devices.
When creating a new group, you will be asked which device to control for which action.
Fusing groups can be useful in situations like when you have a zwave switch and a hue globe and you may want to use the switch when turning off/on or reading the power, but the hue globe when setting the dim/color.

Conjoined Groups
These are groups where you can specify which capabilities you would like to be added to the group.
Giving the most control as to how the group is created.

Alternatives:

The advanced virtual device (part of the Device Capabilities app ) also has group possibilities