Are you trying the tftp updater on a Windows 10 PC? That is known to be unreliable. Windows 7 works OK.
And you are definitely using the Hikvision-specific tftp updater? (copy and instructions inside the download link here:
https://www.ipcamtalk.com/showthrea...are-Downgrader-5-3-0-Chinese-to-5-2-5-English)
I have a suspicion - unproven as I'm unable to test this myself - that some of the previous tftp updater functionality has been removed from the most recent manufacture NVRs.
It would be interesting to hear if this is true from others experiences.
Remember that some months ago Hikvision removed all instances of the tftp updater from their websites.
If the tftp capability has been reduced, the next recourse would be the serial console connection.