You can try to tap the boards together with a hammer and the pry tool that you used to install the boards. However, that only really works if the boards are properly connected but not fully seated.
It looks like the two in the pic are not connected at all and they're just sitting next to each other. In that case you'd have to disassemble the floor and make sure to attach them correctly. It's not terribly time consuming if you don't have to cut any new pieces.
The cheap fix would be to get the color-matching stretchable filler, but those are more used for holes; I think it might introduce more problems when the floor shifts.
If I’ve got multiple places with these gaps am I looking at essentially redoing the whole floor?
If you have these gaps all over, seems like a redo is in order
You can try to tap the boards together with a hammer and the pry tool that you used to install the boards. However, that only really works if the boards are properly connected but not fully seated.
It looks like the two in the pic are not connected at all and they're just sitting next to each other. In that case you'd have to disassemble the floor and make sure to attach them correctly. It's not terribly time consuming if you don't have to cut any new pieces.
The cheap fix would be to get the color-matching stretchable filler, but those are more used for holes; I think it might introduce more problems when the floor shifts.