I am having a problem with a 2.4 site that I suspect is to do with the server, but not sure what to start looking at.

The site was originally 2.4.9 and I just upgraded it to 2.4.13 to see if it would fix the problem (it hasn't).

The problem... I have some custom code for uploading a Gallery Image (FileIFrameField) with separate thumbnail. Some images upload, but a lot don't appear to. By 'appear to' I mean they do upload (you can see their titles in files & images) but they do not show up in the popup box. After you click the 'Upload Files' button it goes through the motions of uploading and once at 100% if you click continue it says that there is no file attached. But this only happens to some images, not all. The permissions of the Uploads folder are set correctly, and this does not seem to be size dependant (won't display a 240kb image, but will display a 650kb one), I have tried renaming the image (the client had images with .JPG as the extension so I have renamed them to .jpg incase that is upsetting it, but still does not work).

The other things that are happening with images are:
1. If I go to insert an image through the wysiwyg editor clicking on the assets/Uploads folder just displays the loading symbol and never shows the images that are in there.

2. With the FileIFrameField if I go to 'Choose Existing' it also just shows the loading symbol and never actually shows the images in there.

3. On the 'Files & Images' tab if you click on the grid icon that should show you the thumbnail, it does nothing. If you click on an image title it opens up the popup but does not display the image.

All of this works fine on my server, just not the clients. So I am not sure what settings I might need to be looking at to see if it needs changing.

Any suggestions would be great.

Thanks
Vix