Frontend does not keep collapsed state for subdevice lists

[NoRi2909]

Checklist

• I have updated to the latest available Home Assistant version.
• I have cleared the cache of my browser.
• I have tried a different browser to see if it is related to my browser.
• I have tried reproducing the issue in safe mode to rule out problems with unsupported custom resources.

Describe the issue you are experiencing

For integrations that support subdevices the Frontend groups all related devices under a single entry that can be collapsed:

That makes it a lot easier to scroll through a long list of devices to find the one you're looking for.

But when you leave the panel and return, unfortunately all the devices are expanded again:

Describe the behavior you expected

Once you have collapsed one device (or all of them) that state should be preserved.
Otherwise that collapse option does not make much sense.

If that's not possible the collapsed state should simply be the default for device lists.

Steps to reproduce the issue

As shown in the screen shots it happens with the Shelly integration as an example.

Here every device is a separate entry and for the Shelly RGBW in 4xlights mode you end up with 5 subdevices (1 + 4 for the channels).

As I have 12 Shelly RGBW in my home it makes quite a difference if you have to scroll just 12 lines or a whopping 72 (header + 5 subdevices each).

What version of Home Assistant Core has the issue?

core-2026.3.2

What was the last working version of Home Assistant Core?

n/a

In which browser are you experiencing the issue?

n/a