How do you deal with someone who gets to a problem and cant figure it out and then just drops it without telling anyone or saying anything, and you dont figure it out for days or weeks?
Personally: I would advice getting lunch with them and getting to know them better. Set up a 1:1 if lunch isn’t possible. Everyone likes honest feedback, or at least a chance to talk about their difficulties in getting tasks done.
If it was important and estimates on how long it will take are overrun, then don't wait to follow up on it and find out how it's going.
Unless the problem is more nuanced like a small component of a larger body of work? Like knowingly leaving flaws in an implementation, or something.
I wrote about once simple process here: http://williampietri.com/writing/2014/simple-planning-for-st...
The key points to keep things on the rails: 1) it's a work queue for the whole team, and the whole team is responsible for every work item, 2) the units of work are small, so they should generally be finished in a day or two, and 3) you to quick daily checkins to make sure work is moving along.
If you add pair programming with frequent pair rotation (e.g., 2-3x/day) then you make it impossible for a person to get stuck for long periods. Even if two people are stuck for a couple of hours, when pair rotation happens then the pair can ask somebody with specific experience to tag in.