I’d suggest trying one of the following IP’s then, there may be an issue with the ones you are using.
play.manacube.net
play.manacube.com
parkourse.com
[gamemode].manacube.com
[gamemode].manacube.net
(For the [gamemode] ones, just put something like Survival, KitPvP, Parkour etc, then you can connect to another gamemode through those with /server or /hub).