Steps to reproduce:

1. Add new host groups
2. Add new hosts and assign them to host group
3. Click on Data Collection -> Host Groups
4. Page does not display list of host groups

Result:

List of Host Groups empty via  Data Collection -> Host Groups

You can however assign a Host Group to a Host and the list shows correctly when performing this function so the host groups exists.
Expected:

Host Groups should be visible via Data Collection -> Host Groups