Guests cannot see Groups Listing (but can view groups!)

Hi Guys.
I've spent the last day racking my brains on this one.

If a guest to the website visits the "Groups" section of my website, they are presented with a blank page (registered users see a list of the groups):
https://guys4guys.social/groups/groups?filter=all

However, as a guest, if they click on a link for a group from a profile, they can view that group (i.e. their not told to login first - this behaviour is as I want, that is, you don't have to be registered to *view* groups):
https://guys4guys.social/groups/groups/item/16-rob-rinder

So my question is why can't my guests view the listing page for groups. This behaviour is also mimicked for Events (although I don't have any yet on the site). So I am guessing there is a common link here, but I cannot find it.

If you wish to go through the process in the same way a guest to the site would see what I am doing, visit the website, look at the top of the page, and you will see a menu bar (Info Menu) where you can click on the "Group" and "Event" menu items.

Cheers
Dave