Remove the jack plate and carefully push the contacts back in. It'll take a little wiggling to get the jack plate off.
It used to happen to me a lot with my 4003 until I read more about the lack of standard dimensioning on what you would think would be "standard" guitar cables. I use a single cable brand now for all of my basses and the loose jack issue has stopped happening on my Rick. Stick with cable brands that use US-made (Switchcraft) or EU-made (Neutrik) jacks, and you should be OK. Stay away from the cheap stuff.