Ok, I’m logged in. The first thing that I see is the the WPLocalPlus Intl plugin is slightly misbehaving. It is loading its CSS and JS and a bunch of other third party JS libraries rather than limiting them to its own admin pages. Generally that is considered bad practice. That could cause a problem or not but it is worth trying to deactivate it and giving it a try.
Guess, not, I tried a small 20 row CSV import and it was fine… though that plugins CSS does mess up the mapping step.
Still seems you were not able to upload the CSV file. Odd because uploading as a txt file always works because they are a permitted file type.
I’ll email you in a second and you can send me the CSV file as a reply.