You might open the file in a text editor to see if
1. there is any extraneous WP debug text getting injected at the start of the file (although there should be protections against that)
2. not all of the output was written to the file (server ran out of memory when generating the file). It would have to be many thousands of rows for this to happen.
Thank you Michael for replying on this. But I still get stuck while I try to fix this. I think I have an issue with the first problem which you talk about in your reply.
But how do I fix this? If you could reply to me, that would be amazing!!
Try temporarily deactivating other plugins then try an export to see if one of them is causing an issue.
Look at turning off debug if it is on. https://codex.wordpress.org/WP_DEBUG
Thank you in advance Michael !! I was finally able to download all my forms.
Have a nice day 🙂
Friendly regards,
Tom