Strange pixelated Chromium in 18.04

After I installed Ubuntu 18.04, I started having this weird problem with Chromium browser (see screenshots). It does not appear all the time however. It happens often when I maximize Chromium from minimized (I forgot if it ever happened when I start Chromium). It goes away sometimes by just scrolling the page, changing tab, or minimizing-maximizing Chromium again.

So far, only Chromium seems to have this problem. Firefox and other software I am using seem to be fine.

So, how do I fix this? Thanks.

EDIT: I don't know if it's relevant, but I am using AMD RX-550 graphics card with built-in Ubuntu drivers (i.e. I did not install any additional driver).

EDIT AGAIN: This problem seems to have stopped after I disabled hardware acceleration in Chromium settings. But still, I wonder why it happens with hardware acceleration enabled.