Connectivity issues with certain individuals

[DemICE 230]

There are certain speficic individuals, with which i have issues connecting with, while with the rest i can do everything perfectly fine.

The issues are:

In an action that specifically targets them,  like a battle challenge, or trade request,  it says the x user was not online.  Same for when the other one tries to request/challenge the other.

In random battle,  the other person is reached,  so i am asked if i wish to challenge them,  and then there is only black screen forever,  while  to the other person the message that x player has declined or disconnected appears.

 

Note that this only happens with certain idividuals and i can't quite pinpoint the issue.