Server experiencing odd network behavior

[gurgle528]

I have a Linux (Debian) server that has some odd behavior. The net graph has "holes" in it but is not showing any loss. The tick rate is set at 50 (and was set at 50 before this started happening).
The server has an i7-6700K and the lag happens regardless of player count.
Additionally, the net graph shows the server's tick rate going all over the place (going above and below 50 by 1 or 2) and occasionally dropping down to as low as 9. I created a script to monitor the server's tick rate and write to a text file if it drops by more than 1 but it has not fired, and I manually ran MsgAll(1/FrameTime()) a couple times to verify it was printing out the same number and it was.
Here's the script for reference:

local function onThink()
	if 1/FrameTime() < 49 then
		file.Append( "tickmonitor.txt", "Tick rate: " .. 1/FrameTime() .. "\n") 
	end
end
hook.Add( "Tick", "TickRateMonitor", onThink )
file.Append( "tickmonitor.txt", "Server started\n")

Shooting guns (we're using CW 2.0) also causes network lag. FPS on both the client and the server remain constant but it seems like network packets just do not get sent.

Here are some relevant lines from the server's config:

sv_maxupdaterate 50
sv_minupdaterate 40
sv_maxcmdrate 50
sv_mincmdrate 33

Here's a picture of the net graph showing the graph saying the tickrate is below what it should be:
[IMG]https://i.imgur.com/0aKsrtF.png[/IMG]

I had this same problem on another machine before for about a month or two with a different host and in a different datacenter.

Also, CPU usage is in check as it never goes above 80% for the individual core it is using (that is mainly when the server has lot of players) and never goes above 12.5% overall usage.

[editline]19th July 2017[/editline]

I managed to fix the 'holes' by adding this to the cfg:

sv_maxrate 0
sv_minrate 800000

However, the server still appears to 'freeze' when players get shot (it is worse with shotguns). The tickrate is still unaffected.

Here's a video showing what's happening
[video=youtube;SZcezYICi84]https://www.youtube.com/watch?v=SZcezYICi84[/video]