Sitemap containing Group not properly handled

[timbms]

Describe the bug When a sitemap contains Group, the watchOS dev app becomes unresponsive

To Reproduce Steps to reproduce the behavior:

1. Include a Group
2. Select a Switch
3. See slaggish response

Expected behavior Snappy response

App (please complete the following information):

• Version [e.g. 2.1.0(12)]

Smartphone (please complete the following information):

• Device: [e.g. iPhoneXR]

Additional context Add any other context about the problem here.

[timbms]

See #535