Does anyone know what this is?

[jahin17]

Found this lodged between the bottom screen, can’t seem to get rid of it, anyone have an idea what it is? It’s bugging me a lot as well.

 

[MrGimper]

Either some glue residue, or a chip. Try running the corner of a piece of paper or card along the ridge/join and see if it dislodges. If not, then return if it bothers you

 

[Pug72]

It'll be a bit of debris picked up, a thin piece of paper as MrGimper suggested will remove it.
It's a great tip for cleaning between the thin gaps on metal links on watch straps also.