this problem just came from one moment to another. I use overleaf + Mendeley Desktop app to organize my references. As I Refresh my .bib file in overleaf there is no more content in it, it seems like the .bib file is empty. On Mendeley there are still all of my references, just not in the .bib file anymore.. I tried unlinking Mendeley and relink it again. Doesn't help.
Thankful for your help Regards, Fabi