I just upgraded to version 5.0.17944.0. Shortly after doing so, I went and marked some of my recurring tasks as completed using the agenda panel on the right side of the main window. After doing this, eM Client suddenly reloaded the agenda panel with heaps of tasks missing.
I looked through my tasks and found that at least some of the completed occurrences of the recurring tasks were still present. Some of the tasks’ due dates have been removed. It looks like every recurring task has had its recurring functionality disabled; they have been converted to non-recurring tasks.
Additionally, various non-recurring tasks are completely missing from eM Client. Thankfully, they are still present when I access Google Calendar directly.