i’ve had lots of trouble with KMC 10speed split links. tried to use 4 so far,
1 fitted perfectly, easy to close, no problems
1 didn’t fit at all, ie, would not close without huge amounts of force, then once closed chain could not pivot.
2 closed with small amount of force, needed a tool to close them, both then cracked / snapped on a ride shortly after.
won’t be using them anymore, have reverted back to using SRAM 9 speed links on my 10 speed shimano, no problems at all and work every time.