Waiting for network in android app


We have our own rocket chat server up and running (v 3.5.2) with a paid ssl certificate. The server can be connected to via browser and windows app.
On android however (latest update from play store) we examine the following: After a while running (I think after rocket chat goes into sleep and is woken up again), the status of rocket chat is on “Waiting for network”. Push notifications are coming to the android device however but the app itself is not updated accordingly. The only solution to this problem is to disconnect from the server and connect again.
Are there any solutions to this?

Any help is highly appreciated.

Kind regards,