Live feed disconnects every few seconds

My network as of now has 30mb down and 30mb upload, and my CCTV has 12 (1080p 15FPS VBR 2030kb bit rate) Cameras hooked up to a DVR, and the DVR is hooked up to an ethernet Hub (connected with 4 other computers on the same network) and then hooked up to a TP Link Archer C2 router. The recorded video on the DVR is completely fine, buttery smooth, but for some reason when viewing live online either from computer browser or mobile app (VMeye / Xmeye) it would disconnect every 3 to 10 seconds, then after a few more seconds it will come back on. It seems like it has gotten worse starting from last week, but I am now trying to figure out if it is a problem with my DVR or my upload speed or my router. What's weird though is that the disconnects are not as often when I lower the encode quality, but it is not completely fixed unless it is on 1 FPS and on the worst quality possible (200kb bitrate). I don't know much about network speed, but I know that 12 cameras x 2030kb is 24360kb so say around 24Mb, my upload speed of 30Mb should be enough right? These computers only check emails and occasionally web surfing, not a lot of uploading or downloading. I have also done speed tests through out the day and it is stable at 28-30Mb upload. If someone could help me confirm that this is an upload problem, then I shall upgrade to 100/100mb, but I'm not sure if more upload speed would actually fix this problem. Any help would be appreciated!

Edit: A port has been opened on the router as well.

I would just like to know if 30Mb upload is enough for these 12 cameras at 1080p 15fps. I'm not sure if my math is right but 2000kb bit rate per camera times it by 12 (cameras), so roughly around 24000kb which is 24Mbit? Can someone please confirm this?

Your Math is Correct. But the math needs be considered of "OverHead" as long as networking is employed in field, say, buffering, duplexing,multiplexing with other sources, etc. You may use substream-compressed bit stream of each camera, not main stream when you are running short of Network Bandwidth.