Maintenance was extended to the server to change provider, among other things. But the problem got worse!
You can not do a challenge mode without the game freezing completely for a few good seconds. This is a problem of communication with the server and not of the users’ internet.
Again, it is impossible to take advantage of the group content on the server currently.
Yes 
The problem is worse now my guildmates do not want to do challenge mode with me because of this.
@chvmbinh0
Thanks for your feedback to us.
Now we are preparing the post about Ping test for SA players.
For that, we would like to ask [SA] Silute players to take a ping test and share their results on the thread.
We will update this reply with Ping test thread soon .
@chvmbinh0
We’ve made the new thread to check your ping.
Please see the below link to share Ping test for [SA] Silute players after 4/10 Maintenance.
Link: Ping test for SA players
game is horrible, please fix, and put more channels