As you can see in the screenshot. I select a file, keep the popup without refreshing the page, and then open it again and the file input is still the file I selected.
<input id="fileuploadbannermobile" type="file" name="files[]">
I try this while the popup is open.
$("#fileuploadbannermobile").val('');
But it doesn't seem to solve the problem.
Setting the input value to an empty string or null will definitely work.
Try setting value to "" or null in vanila javascript
yourInput.value = null
oryourInput.value = ""
Also check that you have set these values to the correct input
It is also useful to know which browser you are using.