I have the same problems, I can only fix it after relogging and relogging. Clearing cache does not work.
I too get the hundreds of gesture loading errors. I havent had the time to take the several hours to deactivate my gestures one by one. I do a few at a time but its a painful way.
I have also noticed the problem is not bound to any viewer. I have had it with Viewer2, Phoenix, Firestorm, Imprudence and Singularity.
I know my problems is not related to the gestures only, I have an inventory of over 55,000 items. Which just seems to be too big to load decently. But I do know that once there is an option to deactivate all active gestures at once, my problem would be a whole lot smaller.