The advice to find the problem by testing is very sound.
I had a similar problem a couple of years ago, which proved to be due to a couple of screws on the keelband that had pulled out.
I hadn’t noticed that the keelband on my boat was in several sections; a short section caught on something, probably the slip while awaiting a trolley, and pulled out a couple of screws. I replaced the whole band, since having it in sections seemed daft, but all that was necessary to stop the leak was to properly seal the screw holes.
good luck