I suspect that when you have a high urgency, the anxiety of having to empty or else gets too much. This may be because you have not yet got "reliable" enough in your peeing at medium urgency. Repetition, repetition till it becomes something you take for granted may help in this.
As for the hierarchy: where is the cubicle door in all this? There is closed and locked, closed and unlocked, and left ajar.
Misfires: accept them as normality, and more common when desensing. A situation that is easy one day, may misfire the next; subconscious issues like mood, tiredness, something about the location that your subconscious has clocked but your conscious self has not. Ride them out. Keep a simple log of each pee, in a coded form that is meaningfull only to you. That way you build up a history of pees that you can look back on. Include misfires if you wish. After a while looking back at the long list of pees and occasional misfires can be motivating.
Human memory of bad events is stronger than for good events. That is why misfires can be destabilising. The diary will help redress that balance by reminding you of the many more actual pees.
Go for it
Responses are not allowed!