I’m sharing this in case it’s helpful to anyone else, having not been able to find much info when we first had the problem (apart from a very old post on here about a puppy called Tilly.) Our puppy Nutmeg started waking up from daytime naps in a puddle of wee - not every time or even every day, but frequently, from when she was about 4 months old. It never, ever happened at night though. Having gone through all the usual tests for UTIs etc the vet decided to scan for an ectopic ureter - he couldn’t see anything on the basic scan and suggested we might need to be referred to a specialist 50 miles away for further tests; we were reluctant to go down this path as it seemed to us that if that was the problem she would be leaking urine all the time, and at night too, and she just wasn’t. Having done a lot of Googling myself, I asked if it could be USMI as that seemed to fit the description - the vet said it was very unlikely in an unspayed puppy of this age, and also didn’t explain why she was dry at night, but agreed to try her on Propalin to see if it made a difference. From the first dose it solved the problem entirely; the vet said that the issue might resolve itself after her first season, and so at the age of 1 we’ve just stopped using the medication as they want to see if it’s sorted before she is spayed. 6 days in and so far so good!! We’re crossing everything that it doesn’t return. 😊 If anyone has the same problem it might be worth mentioning our experience to the vet as it seems pretty uncommon.