Can't upload file

Hello, I just got a new ex2 ultra. I tried to upload files from my computers via the web portal. It works fine on one computer. But the uploading always failed on the other one. I turned on the cloud access and the settings on the two computers are the same. How could I deal with this? Thanks!

Can you upload files directly from your computer (on the same network)?

Yes, the computers are both within the same network with the NAS. I can upload files from one but not from the other.