mistle it seems like your server attempts to run the uploaded PHP files, and it's those files that are throwing an error.
When a file is downloaded in Upload, an internal GET request is made from the download endpoint to the actual resource, which is then proxied to the user for download.
Your log file indicates that while trying to perform that internal GET request, the target file returned a 500 error (which is itself probably logged into the server php or apache logs), indicating that the PHP code in it was most likely executed by your server.
You'll need to disable PHP execution in the assets directory, or use a cloud storage.
