I thought i had this fixed but unfortunately not.
I had thought it was when using a .png file instead of a .jpeg as i get some temporary relief but it's not consistent as jpeg are also now doing the same thing.
When changing the header image i get the following error notice.
Error: Could not calculate resized image dimensions
This happens on all templates.
I have a maximum upload of 128MB so that's not the problem. i would appreciate it if someone can shed some light on this error.
Thanks in advance.