Earlier quoted context omitted.
Well, impossible to say without context. But maybe it is more interesting what you should do afterwards. What did you do afterward?
The project came to an end (hence me having to wrap up their work), so I didn't do much. I'm on a new project now, but I have the same question. If someone keeps insisting their work is coming along great and they'll be checking it in real soon, how do I know if it's true?
"Can you push your work-in-progress branch so I can take a look?"
If they are consistently under-performing you need to structure them. Split larger tasks into smaller sub-tasks that are more tractable over shorter time periods. If a large task is expected to take 3 weeks, split it into chunks of 1-2 days.
That way if a code review isn't sent out you get a quick signal that progress isn't being made.
Remember that as the manager you have authority. They may chafe at being asked to do intermediate checkins and splitting the work into smaller quanta - that's fine, they can grouse about it with their friends, but they still have to do it.
If they are underperforming even within this structure, have them keep a work log - which is basically a 1:1 asynchronous standup with just you and them. Read this work log daily and, in combination with smaller quanta of work, it should be fairly obvious progress isn't made.
At all points don't hide the ball from them that they are underperforming. Tell them that they are underperforming but give them the resources necessary to improve. Solicit their ideas on how to improve and consider implementing them.
Some employees can be structured to improve this ways. Others cannot - you work with HR on that latter group.
But again: as the manager you do not need to see butts-in-seats to gauge productivity. More importantly, it is on you to set a benchmark for productivity and communicate to your team your expectation that everyone hits it, and alert them in your (frequent!) 1:1s when they are falling short.