Good old Premiere reliability at work here?
I'll have a video clip with, say, a few clips above it and in general fairly "surrounded".
But it will have space to move and, at the very least, should be draggable to somewhere else on the timeline.
But it's locked. In fact, all clips on that track become locked. And I can't explain why. I certainly don't use the lock feature on it.
I reboot Premiere, reload the project, and voila- all clips on that track can move again.
What gives? What do you think would cause it to suddenly seize up on a whole track?
I sometimes get this. I find switching to another sequence and back again fixes it.