Didn't see this before I posted mine but yeah same thing has happened to me on a Sunderland save. 14 players out of my 25 man squad have dropped to exactly 4 determination, or on their way there after signing recently. All the players on 4 determination have also changed to spirited personality.
Reading the comments about the welcoming period I'd looked at my team leaders and captains of the 15 month save. Luke O'Nein has 15 determination and resolute personality. Dan Ballard has 14 determination and fairly professional personality. Jack Clarke has 14 determination and a spirited personality (Only welcomed 1 or 2). Anthony Patterson has spirited personality, but is the only player from the original squad to have dropped to 4 determination. It really doesn't seem that bad to have the drops I've had. Hope this is fixed for day 1.