So, it looks like there is a difference in rendering between Ubuntu and Windows, but I can't replicate your problem specifically.
I'm dual-booting Ubuntu 18.04 and Windows 10, and in Windows 10 I see the following:

AFAICS, it looks fine and just as it always has.
In Ubuntu, I get this:

Which looks oddly compressed in some way. Admittedly, I'm not sure what the Prime Post looked like in Ubuntu before so can't confirm whether this is similar or different.
In both cases, I'm using Google Chrome (not Chromium) 68.0.3440.106. chrome://version output below:
Windows 10:
Google Chrome 68.0.3440.106 (Official Build) (64-bit) (cohort: Stable)
Revision 1c32c539ce0065a41cb79da7bfcd2c71af1afe62-refs/branch-
heads/3440@{#794}
OS Windows
JavaScript V8 6.8.275.26
Flash 30.0.0.154 C:\Users\willi\AppData\Local\Google\Chrome\User Data\PepperFlash\30.0.0.154\pepflashplayer.dll
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36
Ubuntu 18.04.1:
Google Chrome 68.0.3440.106 (Official Build) (64-bit)
Revision 1c32c539ce0065a41cb79da7bfcd2c71af1afe62-refs/branch-heads/3440@{#794}
OS Linux
JavaScript V8 6.8.275.26
Flash 30.0.0.154 /home/wkumler/.config/google-chrome/PepperFlash/30.0.0.154/libpepflashplayer.so
User Agent Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36