The long edges separating or are the short edges? My guess from what your saying it's the short ends.

It's likely that the floor has too much variation and or the planks are being pinched under moldings or cabinets. Both will let the plank full apart, if it's pinching by moldings or under a cabinet that's a solvable problem with gel superglue (after fixing the problems origination). If it's the floor is majorly uneven like there is a hump or dip.. that's a problem than cannot be easily fixed superglue might hold it together but it might just change where the problem is manifesting.

Nailing a floating floor down is not a recommended fix and most times will just make more problems.