JS: Grid Format in Tabs
You will need to place this custom js in your theme. Usually themes have a custom js area or if not you can find some free ones in the wordpress repository.
Replace the class .yourClass with your navigations tab class name. We realize this may not fit your exact requirement and you’ll need to change a few things around in the code below if you are not using a ul list in your tabs, however this is a good starting point to search for other answers on the web should this one not work. The idea here though is we want to set a timeout function so we can trigger a window resize which in turn will make the images show up properly.