Yandex Disk upload speed is about 100 kbps

Hello! I’ve just upgraded to professional edition to be able to upload to Yandex Disk but upload speeds are horrible. When I start uploading the speed is around 20 Mbps for 1 second and then drops to 300 Kbps and stays there. Official Yandex Disk app let’s me upload and download at about 50 Mbps. Is it some kind of API restriction or a technical issue? Please let me know if you need logs or anything else from me.