Hi, I think I found a solution. Removing WP-SuperCache and following this procedure allowed me to bulk upload images and retain their size data.
WP Super Cache was removed from your blog but the mod_rewrite rules
in your .htaccess were not.
Please edit the following file and remove the code
between 'BEGIN WPSuperCache' and 'END WPSuperCache'. Please backup the file first!
WP Super Cache Plugin
I had to manually uninstall SuperCache via FTP after changing temporarily the folder to 777. It appears something in super cache is interfering with the uploads.
I believe this was installed automatically by my host when installing the WP for this site. Pair does not use cPanel but SIM installer. Apparently the code for these host install programs may be causing trouble with 3.8?