When wiki page group mode is set to either 'Visible groups' or 'Separate groups'. The groups selector displayed on wiki/view.php page (a) does not reflect the current group (b) changing the groups does not bring you to correct group page.

The investigation identified the following issues:

1. The current activity group in wiki view page is not updated to selected
group in most cases, making dropdown menu displaying the wrong group. Having
said that, the displayed page may also belong to the the wrong group, I have seen a
situation that after selecting group, both dropdown menu and page do not match
neither each other nor the requested page.

2. I guess the wiki title is sometimes malformed for groups (spaces in the original title are replaced with +), which makes it redirecting to the
'first page', and even causes 'redirect loop' or prompting for group page creation (while it has been created already).

3. The title used as hidden parameter in group dropdown always reflect the title of the previously selected page, so the attempt to switch group ends up with non-existing page and redirect user to 'first page' (which might even be not the main page either).

Replication steps:
(all steps are done as admin)

1. Create collaborative wiki activity with 'Visible groups' and leave page name default ('First page name')
2. You will be prompted to create the first page, write 'first page' in the content.
3. Create two course groups, Group 1 and Group 2.
4. Go to the wiki activity and select Group 1
5. You will be prompted to create a new page 'First+page+name', write 'Group 1' in the page content.
6. (observation 1) You are now on the main wiki view page, the page content belongs to group 1, but selector reads 'All participants'.
7. Select 'Group 1' in dropdown selector.
8. (observation 2) The content now switched to the 'first page' and the selector reads 'All participants' - 'Group 1' selection failed.
9. Select 'Group 1' in dropdown selector again. Now display seems correct - Group 1 page is displayed and selector reads 'Group 1'
10. Select 'All participants' in dropdown selector.
11. (observation 3) Chrome browser reports 'This web page has a redirect loop'
12. Get back to moodle from error page (just open the url and the course page), click on wiki activity we created.
13. (observation 4) Wiki prompts you to create the new page 'First page name'
14. Proceed creating it, the surprising thing is that it will belong to 'Group 1' as well under different name, so name it 'Group 1 new'.
15. Now try switching between 'Group 1' and 'All participants' several time, you will be able to spot all three pages one after other, but in most cases the displayed page and selector will not be reflecting the one you have chosen.

If you like to observe even more weirdness, you may introduce a second page by selecting 'Group 2' in the menu, and play switching between them.