Log is empty.

[Mygunship]

The log would disappear after PoE Whisper has been open for a while.

[Kapps]

Hmm, haven't been able to replicate this, but haven't really played PoE lately. Gonna try leaving it on a while and see what happens.
What happens if you try scrolling up? Like click in the log and press up arrow a few times or something.

[Mygunship]

It just happened to me again. Scrolling and pressing the up arrow shows the previous line of message. You can press the up arrow until all of the messages are shown.