This is most likely a symptom of antivirus software being a pain in the head. Please update the software to check if that helps. If not, please check if your antivirus software uses a Webshield function and turn this off during the upload.
With Bitdefender, disable the SSL function in the setting Web Protection to make your uploads work again.
It could also be a firewall that's causing your transfer to stop after attempting to upload for a short time. In this case it's important to whitelist our service. If you need help whitelisting, please visit this article for more information.