What Type of Coaxial is this?
(Memorializing the answer I suggested in comments, since OP says it’s correct)

If it looks like RG6 and an RG6 connector is hard to slide on, then it’s likely RG6Q or quad shielded RG6 cable.  You’ll need a connector marked for RG6Q, such as this:



RG6 and RG6Q “look” very similar but the specs are different enough to require RG6Q connectors.  (Also RG59 is much smaller than RG6 so if you’re having trouble getting an RG6 connector on then it’s most likely quad cable.)