New router blocking uploads

Hi. Wondering if anyone can help. I have a RUT 901 router housed in antenna on our roof. I previously had a RUT 950 – the lengths we go to get wifi in our remote location! Since switching Ive noticed on some programs it does not like to upload files. For example, on my Slack app it won’t let me upload/share video to my colleagues, but will allow voice notes and images. Also noticed that it will not upload to wetransfer. Sometime refuses to send large emails etc.

Im not that tech savvy - a friend help me set up - but any ideas what it could be? All used to be fine on the old router. Could it be a firewall setting, or IPV issue, or need of a firmware update, or just a simple restart?

Trying to bump this up as I really could do with a hand! It’s so annoying…