Thank you for your reply Gaetan_BRISSARD and for confirming you will try setting the player window size to see if this resolves the issue.
When you reinstalled the player before, did you also remove all traces of Xibo, including the previous local library and any other remaining files?
I have also been discussing this issue with my colleague, who reminded me of an issue previously seen on Windows which would cause the player window to shrink based on the display settings stored in the Windows registry. Below is a link to the guide for that issue, which explains where to find those stored entries. In case this is somehow related to the issue, I would also recommend taking a look at this guide and following the steps. Please note that the settings in the guide refer to a full HD resolution, if you are not using 1920x1080 then you will need to adjust those values to match the resolution of your display.
Many Thanks.