I've had the same issue since I received my Sense in March 2022. Slow charging message appeared every time I plugged it in, no matter what I did -- and took hours to fully charge.
After my watch completely broke when taking it in the pool for less than 15 minutes (wasn't even swimming, just playing with my kiddo), I called Fitbit to get a replacement. Told them about the charging issue and he asked if all 4 prongs on the back were the same... can't believe I never noticed, but one of the charging prongs had sunk into the charger, therefore not making a solid connection. They immediately sent a new charger, along with a new watch face.
It charges much better now, though I'm noticing one of the prongs is starting to sink into the charger again. I'll keep reporting this issue and Fitbit will have to keep sending a new charger, until they fix this. Can't imagine they don't know this is happening.
