First, please try clearing the cache of your browser including Local Storage (this is crucial). Wise Chat Pro uses cache to store some part of its temporary data. In a very rare cases it requires to be cleared manually.
If this does not help please follow these advices depending on your configuration:
A single public channel configuration.
Please make sure that this option is enabled:
Wise Chat Pro Settings -> Appearance -> Auto-open First Channel
This will open the public channel automatically and prevent from closing it.
Multiple public channels configuration.
If you enabled the option:
Wise Chat Pro Settings -> Appearance -> Auto-open First Channel
then the first channel should be opened automatically. If you close every channel (both public channel and private chats) then you should get “No channels open” message. It is normal.