Increase In Customers Reporting Error With Product File Uploading

Our website offers a lot of products that require the uploading of an image to add onto a custom product.

We used to get the odd customer email us and say that the website was reporting that the products could not be added to the cart and to check that the images meets the minimum requirements etc. In most cases people would email us the image, we would open it and re-save it and then email it back to them and it would work without issue. We simply put it down to corrupt images as there never seemed to be any consistent cause such as browser/device etc.

However since upgrading from 4.3.4 to 4.3.9 we have noticed a marked increase in customers experiencing this problem and it really does not seem to be consistent. For example, a customer (customer 1) sent us an image and we too could not upload it with the standard error they where getting. We opened/re-saved it and sent it to them.... all good and uploaded fine and order was as normal.

However another customer reported the problem today so I tried some more tests and I could not replicate the error. In fact I even uploaded the image that customer 1 originally sent and it uploaded fine.

We have noticed a drop in customised orders since upgrading and I getting a tad paranoid that the error is more prolific that I may have thought... especially as traffic has not reduced.

With regards to settings, the max upload in PHP is at 30M and there are no restrictions in CS cart with regards to the file types (that I am aware of, certainly nothing in the file type for options).

Does anyone have any ideas or advice on tracking down the issue?

[added] The reason I have have not been able to replicate this is it appears it may be product or option specific. If I try and upload what I thought was a corrupt image too one product it is fine, but not on some others - even though they are the same image. I have also found that if it fails, click the x to delete it and trying again makes it work.