I've read that the Montreux Volley Masters is scheduled in mid-May this year. It was an article on the swiss federation site which mentioned that the Swiss NT will play two tournaments before the ECH: Montreux and the Universiade.
The Montreux Volley Masters 2019 is from May 13. until 19.
Participating teams are: China, Germany, Japan, Poland; Italy, Thailand, Switzerland, Turkey