Why does the upload progress bar reset at 40% when uploading large files?
I was able to fix the Upload Progress so that it didn't stop at 40% (2 GB).
This is a temporary fix:
I uncommented the ondrej repo in the sources list (/etc/apt). This gave me access to uploadprogress 1.1.3-3 which has a couple of patches that the PECL repo doesn't have.
Then I got the source code:
apt source php7.3-uploadprogress

cd php-uploadprogress-1.1.3

And changed:
int read_bytes;

to:
unsigned long int read_bytes;

and recompiled from the source:
phpize; ./configure; make; make test; sudo make install; sudo service apache2 reload

It seems like the references to int were all changed except the reference to read_bytes. The maximum value of an int is 2GB.