The CCTV box is the Hikvision DS-7608NI-I2-8P. I've been in touch with the manufacturers about this, but haven't had any solution from them. I figured that it could be a VLC issue, but not sure.
I'm still trying to post a bug issue, but I cannot get into the Videolan issues board. I try to sign up, but the verification E-mail doesn't get sent to me! I'll try it again today.
I checked through the user manual this morning, but there isn't much in the way of troubleshooting I'm afraid. The only relevant info I could find re: the frozen image is this one.

(click to enlarge)
But the fact that it's there at all implies that it's a regular occurring instance to my way of thinking. Here's the
link to the manual.
Here's how to run
CHKDSK on the HDD to eliminate the drive as the cause of the problem. If you're going to run it from an elevated command prompt just run
chkdsk /f which will fix any errors found. If there's a bad sector on the drive run chkdsk /f /r
The videoland issues site changed recently and the new one is a pain in the posterior I regret to say. It uses 2FA, but my phone which admittedly is a bit dated doesn't support QR codes. So although I registered username and password I couldn't go any further with it. You might be in the same boat.