When an external sender sends a calendar invitation, I receive an email where I can add the event to the agenda (see button "ajouter à l'agenda" / "add to calendar").
When the external sender changes the date/time of the event, I receive an email about the modification, but I cannot add the modified event to the calendar (no button is present).

The event I have in my calendar and the one proposed by the external sender are thus out-of-sync, and because no "add to calendar" button is present, I have no way to sync them back.

If I reload the page (Ctrl-R), the "add to calendar" button is still missing. Same if I log-out and on again.

[If I delete the event from my calendar, I still see no option in the invitation email to add it to the calendar. Clicking the "reload" button on the SoGo interface doesn't help. If after this I perform a full refresh (Ctrl-R) of the page, then I can add the event to the calendar again.]