In Documents\Rack2\settings.json, do you have a section like this?:
"windowMaximized": false,
"windowSize": [
2169.0,
1313.0
],
"windowPos": [
211.0,
115.0
],
If so, and the numbers don’t look sensible (like, they’re negative or huge) then kill any Rack processes and remove that section. Or just rename the file, and Rack will recreate it with its default settings.
Upgrading Rack might also fix it - there was a fix put in after 2.0.2 that relates to this.