Note- we took apart the shower pan and whoever installed it used parts for the kitchen sink such as a flexible hose... Thanks everyone for your help, and you were right/ it was a bad install...
While i was plunging out a shower in Spain, blue thing came out of the shower outlet.
It looks a bit melted, I did use drain cleaner on the shower a few times. There are some supicious marks on it that might indicate it was under compression and some old sand on it that has engrooved a bit. It looks stretched and melted. But since its melted looking I cannot tell for sure.
Is it possible this ring connects something and came loose or is this more like a situation where someone dropped something in there on accident? note that the measuring stick in the picture is in metric
I googled for blue plumbing rings and only saw a blue product in image below, but not sure if it's this, its blue and maybe the wrong size. (from spanish website, european measurements)