Tin wires but not the connection point. I'll try that.
Also worth keeping in mind the connector's a far greater thermal mass (that needs heating up so the flux cleans its surface and the solder sticks).
Although I haven't tried tinning the connection point I noticed that the solder doesn't really flow onto the connection point but stays more as a bubble on top.
How are you applying the solder to the connector, then?
"Solder on the iron tip, then apply tip to connector" = rookie mistake

Yes, you wanna tin the tip so whatever molten solder is there, offers an increased AND flexible thermal contact area, BUT after touching the tinned tip to the connector and warming it up, you also wanna feed fresh (flux-cored) solder, for the above-mentioned reasons.