Ever look at the old masters doing kata and marvelled at how incredibly smooth their motion was? Ever marvel at their amazing ability to stay right in perfect synch with uke the whole time? Ever compare your own skill to theirs and think, "Boy, I suck!"?
Sometimes (maybe even often) it seems like when we get to trying to synch with uke, something interferes. There is some sudden discontinuity and by the time you figure it our and switch tracks, uke's gone.
If you've ever wished that you could get in synch with uke and stay there longer, I have bad news for you. The world ain't like that. About the best that I can do under pressure against a non-compliant partner is about two synchronized steps with uke, and I suspect that even the folks that are way better than me can't maintain a nice, constant synch much longer than that. (Of course, if someone were able to reliably maintain a synchronized state for three steps, that would make them 50% better than me, and in a fight 50% might as well be infinity.)
But my point is, I don't think that its realistic or healthy to beat oneself up about the disequilibria that pop up in the uke-tori relationship, because those disequilibria are just part of the nature of the thing. It seems to me that synchronization (kimusubi) mostly happens in short snatches here and there amongst the motion between uke and tori. A much healthier, achievable, and still functional skill level is being able to synch with uke for a step or two, then when it goes to chaos, follow along, keeping yourself safe until you recognize another step or two of synch.
Now, we do often try to train in large, drawn out arcs of equilibrium even though that isnt how the world works, but this is because we think that this is a pretty good way to train beginners to recognize little pieces of those arcs when they occur.
Even though its easier to learn to see these things in the long arcs, you should'nt beat yourself up about your inability to find one of those long arcs in randori. It's definitely a good thing to step out of the long, beautiful kata arcs into the punctuated equilibrium of randori - and to practice that way frequently.