Leaky Lab :(

[Darleina]

Hi Everyone, new on this site but I have a question and would love some help with it.

We have a 14 week 2 day old CKC reg Yellow Lab male pup named Porter (Whew that's a long title)!
He's was doing great with housebreaking- no accidents in weeks, when suddenly in the last 2 weeks, he's started to mess just a little in the house. He might be playing and suddenly pee a small amount (maybe 100mL) or he could be quite settled and just happen to be walking and leak some. He keeps walking as if he hasn't noticed and leaves small droplets in a trail.

Why is this happening? Is his urinary tract just not caught up with him yet as he grows suddenly? He is capable of holding it all night or for 8+ hour when in his 4'X8' indoor dog run while we're at work and he signals for the door regularly and we let him out. But he might only have been back in for 15 minutes sometimes when this happens. Please help!