I can confirm this resolves my issue described above. Just delete the eventcalendar plasmoid and you could still reinstall it at the end of your manjaro update (restart).
Why could eventcalendar create such a big issue?
On a side note, the recent update also gave me headache with Compositor and Latte-dock which is luckily easy to resolve:
System settings > Display configuration > Compositor > uncheck Allow applications to block compositing.