Comment 5 for bug 1721117

Here is some analyze of those extension:

* move clock doesn't work due to those lines:
    // do nothing if we're not in user mode
    if ( Main.sessionMode.currentMode != 'user' ) {
        return;
    }

To allow people using the upstream vanilla session, we have an ubuntu mode, inheriting from the user one. However, the mode name is different. Different fixes:
-> you can poke move clock upstream to use a blacklist isn't of a whitelist (disabling under kiosk and gdm mode for instance)
-> you can ask on gnome bugzilla for the shell to expose the inheritance hierarchy to extensions, and they can check if they are in the user mode that way. Then extensions will need to be updated as well.

* Activities Configurator doesn't work because it relies on the hot corner that we disable in the ubuntu session. I think poking upstream to get that optional would help (especially as there is some chance to have that configurable upstream, we took an upstream patch not committed yet).

* Activites button text (both extensions) don't work either on a vanilla GNOME session. The name property as changed in GNOME Shell 3.25.9x, and so, the code needs to be updated. This isn't related to the ubuntu session.

So, in summary:
Only "move clock" and "activities configurator" don't work in the ubuntu session only, but both has to be upstream extension fixes. If someone wants to poke the upstream extension maintainer and point them to this thread, that would be great.
The 2 other "activities button text" extensions are broken in GNOME Shell 3.26, in both sessions, and not related to any ubuntu change. Upstream needs to update their extensions to work with the new GNOME Shell version.