Hi there!
I had a problem with my playlist too. I left it on the other screen and then I never had no opportunity to reconnect the monitor.
In %AppData%/(roaming, on newer win)/BSPlayer/bspml.xml has the information. The file bspml.xml contains a lot settings about the media library and below contains data for the playlist.
It has 2 coordinates: <PLLeft type="int">0</PLLeft>
<PLTop type="int">0</PLTop>
If you change the values to 0, the playlist will appear in the top left corner of your screen.
I'm glad if I helped.
Have a nice day!