Unnamed White Box Appears on my Mac screen

posted by someone else earlier with same

Summary :

• A random, unnamed tab/window appearis on my Mac screen intermittently.
• The unnamed tab is mostly empty, featuring only a close button at the top right and a small "[x] Close" link at the bottom left (attached screenshot)
• It has no title, and I can't locate it in the "Force Quit Applications" menu.
• Is there a way to identify which application is causing this? How can I remove it?
• It closes if I click "close", but randomly reappears.