Invisible pieces

I had two consecutive games today where some of the pieces were invisible. I played games in the same browser window earlier this morning, without any problems. Any ideas why this might have happened?

Screenshot:
Browser: Safari Version 11.0.2 (13604.4.7.1.3)

We had this really often, I fell victim to that a couple of times. Win10, Chrome.

Mostly the bishops were invisible, even in the captchas...

I had this happen in Safari. I think it is a browser issue. it seems that Lichess is tested with Firefox. Try using Firefox.