Xordrive.io upload error

Hello, I have a following problem: if I upload a file using the mobile Internet (3G and 4G), then the upload periodically goes to a backward position and then I get an exclamation mark icon.
With WiFi (it’s slow at me) only sometimes the download goes backwards. I’ve been using this storage since November 2019 and I even store big video files there. I’ve never had this problem before.
There are no such problems with other cloud storages right now.