It sounds like you're throwing three times, correct? In your head you're thinking "One, Two, Three" and you stop. I did the same thing. Count out loud, and then count "One, Two, Three, Four"
Try to break out of that three count rut gently. Once you're stuck on four, you're already juggling, so stop counting and get on with it!
I do the same thing on the guitar and other things where we get stuck in patterns. If I want a smooth arpeggio with no discernable breaks between measures, I count one beat more until I get over the rough spot. So, instead of 1,2,3.. 1,2,3.. 1,2,3.. 1,2,3 it becomes 1,2,3,4.. 1,2,3,4.. 1,2,3,4.. or I count 4 but keep the 3 beat : 1,2,3.. 4,1,2.. 3,4,1...2,3,4
Same number of notes but the counts are different. Eventually the gaps fill in and I get 1,2,3,1,2,3,1,2,3,1,2,3 without having to even think about it.