changes in configuration are not taking effect
Installation and Configuration
your php.ini file does have 2048MB for all 3 of the necessary items:
post_max_size = 2048M
upload_max_filesize = 2048M
memory_limit = 2048M
and your SYSTEM CHECK tool shows that it has that limit working. (screenshot)
But its not working, there are no errors, and it fails almost instantly on files larger than 512M. It doesn't even try to upload them partially.
I've replicated your php.ini setup here on my local environment but can not reproduce the issue. For me it does work.
That suggest something about the server is the issue, but I do not know what sorry.