Is this a feed issue or funky chicken butt?

[PoppasGrill]

We got a strange egg yesterday.

It’s from one of our older ladies. 2-3 year olds. Or at least was in the nesting box in their coop and was laid late in the day as we collected eggs around 2pm and found this one near lockdown time.
Is it a high calcium issue, we do use layer feed mixed with scratch and treats, and have shell on the side.?

 

[OrpingtonManiac]

https://www.backyardchickens.com/articles/common-egg-quality-problems.65923/

 

[PoppasGrill]

https://www.backyardchickens.com/articles/common-egg-quality-problems.65923/

Thank you
Am bookmarking this for future reference.