I am trying to: upload a featured image (or any image) on a post form
Link to a page where the issue can be seen: hidden link (you need to login to see this form)
When logged in, choose "Create a Seed Packet" from the "Seed Packets" menu then try uploading a jpeg file with the "Choose File" button under "Seed Packet Image" label. You should get the error dialog.
I expected to see: a successful upload of a featured image to the form
Instead, I got: a message that the upload failed
This worked fine on CRED 1.9. I updated to 1.9.3.1 and it no longer works. The problem occurs on hosted site and on localhost where I only have Toolset plugins installed with PHP 7 and Toolset Starter theme. Localhost allows plenty of PHP memory (not sure about hosted limits) so I don't think that is the problem. Uploading from admin screens works fine. It is just the CRED forms that fail.
That will create a debug.log file in your wp-content directory which you can examine in any text editor. Try visiting the page with the form and uploading an image again, then inspect the log. If you don't find the debug.log file it means it didn't generate any warnings or errors.