Continual Error Using WordPress Importer

I am trying to import posts from one WP site into another. I have exported the posts from the old site via the “Tools” section and attempted to import them into the new site using the WP Importer and instructions at https://codex.wordpress.org/Importing_Content#WordPress.

However, I am continually getting the following error: “Sorry, there has been an error. File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your php.ini or by post_max_size being defined as smaller than upload_max_filesize in php.ini.”

I have checked, and also contacted my hosting provider to verify, that uploads are allowed and that max file size will accommodate the file.

The file is not empty. In fact, 10-15 posts do successfully import every time. However, I am attempting to export roughly 400-500 posts and the resulting export file is only 2.10MB. I would have expected it to be much larger.

Any help with this issue would be greatly appreciated!