Why does my router keep resetting my device name?

[#1]

I have a port redirect set on my router to redirect to my NAS which is called BRYNAS1.  Every few months, this device name gets reset to 'unknown' therefore making the redirect fail and the web site hosted there inaccessible.  Why is this happening?  Does it coincide with Plusnet updating the router software?

Any ideas?

P.S. I have a fixed ip address.

[#2]

Moderators Note

This topic has been moved from Broadband to My Router