The Mendez-Laing situation won't have helped, whatever the reasons for his departure. Although I believe it was right for Etheridge to leave, I'm pretty sure he was well liked by his teammates. Paterson was a big character, so no doubt his sale has had an effect. Tomlin's absence is another obvious negative.
Could be that the spirit in the dressing room isn't quite what it was, but it's obviously the manager's job to sort that out.