What can cause interruptions in the work of the samba / dlna server (on the router)?

Question

DLNA

Hello, a WD terabyte is connected and shared to the Zyxel Keenetic Giga III router, until recently everything was perfect, but now troubles have begun: periodically I can’t go there via smb, and the server is visible, but inaccessible (on the phone in ES Explorer and on computer c win7 is in the "Network" tab, but when I try to go there - endless loading). At the same time, there is nothing suspicious in the logs of the router. If you log in via FTP, everything seems to be ok, but when playing the video, it freezes every 2-3 minutes, and messages like this appear in the logs

Aug 11 12:57:37 pure-ftpd
([email protected]) [INFO] Can't change directory to /E80C0A400C0A0A70/Downloads/Dark Matter 3 - LostFilm.TV [MP4]/Dark.Matter.S03E12.720p. WEB.rus.LostFilm.TV.mp4: not a directory.

I tried to raise the DLNA server, apparently, it has the same problem as with samba, and in the log there are errors similar to ftp errors. Suggests that something may be wrong directly with the disk, although there are no obvious signs of its death (sounds).
I am attaching the log for a few days .