Why does an external drive slow down at a certain percentage of filling?

Question

Hard disks

Hello. Home media center based on Zyxel Keenetic Giga2 router and Seagate 3TB external drive. It works fine as long as the amount of data on the disk does not exceed 1 TB. When exceeded, brakes and suspensions begin. The TV plays the files, but it is impossible to access them from the computer, move, rename, play back, when you try, the computer thinks for a long time and eventually goes into itself. The router issues the following log:
kernel: tntfs error (device sda1, pid 339): ntfs_bio_end_io_read(): Bio read I/O error.
The disc is brand new, just bought. Tell me, can something be done about this?

Answer 1

Immediately I ask you to perform the simplest manipulation: connect this hard drive via USB to a PC and try.