Yes I agree. I think a reason is you haven't developed a center. Your upper body is stiff but all you posture is sloppy. You are collapsing into yourself. I'd suggest to practice a lot of weapons regularly.
Other suggestion would be as a uke to push your center constantly toward nage center to create a continued pression on his structure in any moment of the technique. You shoul do it by constantly bending your knees and use big muscles of the legs, make sure you can freely move your shoulders in any direction anytime.
Mentally you seems to be afraid by a nage.....there is any reason?
Thank you, Szczepan! I'll try to do that. No, I don't feel afraid; in fact, as uke with Sensei I feel about as safe as possible (even when I have an injury of some kind). I am trying to treat the connection like nage could explode in any direction, but maybe too much. Also, it had been a couple months since my last training and that was one of the more stressful periods of time I've had in a while so that might have had a little to do with it, too. Whatever the case, I'll try to be more mindful of it. I think a general theme I'm seeing so far is that people would like to see uke be more assertive.
Thank you again!