Maybe small bug?

[sampaperton]

[19:25:28] Try to catch Pokemon (0) with Ultraball...
[19:25:28] Pokemon fled.


just throwing it out there.

 

[pokelohm]

I experience this bug as well. Not sure if it consumed an ultraball or not so I will keep an eye out for it if that happens again.

 

[HatchingEgg]

Yes you found a bug. It was confirmed from other users also. It will be fixed.