Descriptive Problem Summary:
So i noticed that sometimes when i changed client pixel offsets stuff with visual contents could stop displaying them, and it's inconsistant too, sometimes couple of tiles breaks, sometimes whole screen worth of vis_contents stops.

Things to notice:
This was experienced by all players that played on my server, at least once.
This also occured upon rapid elevation through z-levels back and forth
This is/was happening to overlays as well, but far less often.

Numbered Steps to Reproduce Problem:
1.Have alot of vis_contents
2.Start changing your client's offset in controlled manner
3.At some point it will start to breakdown
(I also think you should host the server with dream daemon for this.)

This is how it looks
https://cdn.discordapp.com/attachments/323648342099886090/ 670696993722597376/unknown.png
https://cdn.discordapp.com/attachments/323648342099886090/ 670697283129573396/unknown.png

Code Snippet (if applicable) to Reproduce Problem:
I can provide you with "testing enviroment" instead:
https://dropmefiles.com/RmWec

Does the problem occur:
Every time? Or how often?
It's inconsistant, but everyone had it at least once per game.
In other games?
Yes, i tested it both in my game and in testing enviroment.
In other user accounts?
Yes.
On other computers?
Yes, all of my players experienced it.

When does the problem NOT occur?
Well i don't recall vis_contents/overlays breaking down upon normal camera movement at all, only when it's instant or so.

Did the problem NOT occur in any earlier versions? If so, what was the last version that worked? (Visit http://www.byond.com/download/build to download old versions for testing.)
I haven't tested it on older versions but i think i've seen this long before 513.

Workarounds:
No workarounds i know of, unless you're not offsetting client's camera it will happen.