Short answer
Check the source is visible and above your game in the Sources list, that the URL or file path is correct, and that Width and Height aren't tiny. Then right-click the source, choose Properties and click Refresh cache of current page. If it's still blank, toggle browser hardware acceleration and restart OBS.
Step by step
Is it supposed to be empty?
Alert boxes, goal popups and some chat boxes are transparent until something happens. Send a test alert or a chat message before assuming the source is broken.
Check visibility and order
Make sure the eye icon next to the source is on, and that the source sits above your game and camera in the Sources list. OBS draws the top of the list in front.
Check the address or file
Open the properties. A URL should be the overlay or widget URL, not the editor page from your browser's address bar. For Local file, check the file still exists at that path; moving or renaming the folder breaks it.
Check the size
Width and Height should match what the widget was made for, usually 1920×1080 for a full overlay. If the size is small, the content may be drawn outside the visible area.
Refresh the page
In the properties, click Refresh cache of current page. This reloads the page and its files, which fixes most widgets that stopped updating after a change.
Toggle hardware acceleration
Open Settings › Advanced › Sources, switch Enable Browser Source Hardware Acceleration off (or back on), and restart OBS.
Still blank?
- Open the URL in Chrome or Edge. If it's blank there too, the problem is the widget or its settings, not OBS. For StreamElements, check the overlay was saved.
- Delete the source and add it again. A fresh source clears settings you may have changed by accident.
- If the page went blank after you switched scenes, untick Shutdown source when not visible.
- Check your firewall or antivirus isn't blocking OBS.
Alerts show but make no sound
Tick Control audio via OBS in the browser source and check the source isn't muted in the Audio Mixer. With that option on, set its audio monitoring under Advanced Audio Properties if you want to hear alerts yourself.
