Sorry the birds tended to hide among the stones and driftwood, so hard to get a photo of them together. But I attach a different angle of the mystery bird and one of the 'normal' looking Purple Sandpipers. All the others looked like this one, and the mystery bird was obviously paler and brighter coloured than all the others in the group.
I'm struggling to find any reasons why this isn't a rock sand.
I've added a link from the European Rarities thread too with a request for comments.Me too.
Recommend changing the thread title to reflect a possible Rock Sandpiper in the WP - that'll get a lot more views and maybe some folk with more experience.
What about Dunlin x Purps hybrid? Is that known at all?
https://www.birdforum.net/showthread.php?t=169428&page=253&highlight=european+rarities
post 5058 - didn't have the time to scrutinize all characters and also lack personal experience with rock sandpiper, so i'm curious of the outcome and hope that a wader expert from the other side of the pond could give his/her expertize!