I've come across this 2-3 times in about the last time (last time 2-3 weeks ago, except today).Attachment 230369
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I've come across this 2-3 times in about the last time (last time 2-3 weeks ago, except today).Attachment 230369
Attachment 230370 like this
and this Attachment 230371
After restarting the game, "this" disappears
First guess is something is wrong with your device - memory corruption, overheating, etc, since there have been no other reports of this.
You might try a different browser, but it still looks like memory and/or graphics corruption to me, so more likely a hardware problem than software.