I had a similar problem with 10 speed quick links I bought from Decathlon recently, pretty sure they are KMC links rebranded as B’Twin. It was the same problem, just a tiny bit too short and I couldn’t fasten it once it was on the chain. I had another 10 speed link lying around and putting them next to each other, you could see the pin was shorter.
Decathlon have since said that the links are for SRAM chains only. I’m pretty sure CRC were selling different KMC links for Shimano/SRAM chains, but it seems to be just one option for both now.
On a related note the last KMC links I bought I couldn’t get to close even off the chain…