Only familiar with much, much smaller boats - but that's not unusual for station-keeping (or anchoring, but I expect a moon-shaped track at anchor). To be super clear, I'm extrapolating from 30ft boats, I could be wildly wrong in any of this.

In a nutshell you don't stay still, you drift around with wind and currents (and breeze-block shaped ships have a lot of windage!). So you drift off station, motor back, rinse repeat. ('Station' is usually a box you're bound to rather than a point you try to hit, for exactly this reason)

Anchor isn't much different - a cargo ship in an anchorage isn't a static fixture, it's realistically the world's largest windsock.

Compare another ship waiting in the same area - https://www.vesselfinder.com/?imo=9811000 Hit the "Track" button on the sidebar (under the photo of the ship), and you'll see a similar history. Theirs is tighter, but that could simply be a product of it getting crowded. I'd expect EG's arrival to be more planned, less chaotic - arrive, assemble the convoy, join the queue and go.

It's the GPS position transmitted via AIS, it's like your phone while you are in a static position but on a bigger scale...