Check the clutch cable adjustment right by the clutch lever on the handle bar.
It may have loosened up causing the slop you are getting when going through the gears when you are riding. It happened on my bike before.
I get a little bit of it as well just after I change the oil too but as the oil wears in (I guess) the slop in the clutch gear changing goes away.
But check your clutch cable first from the handlebar all the way down to where it ends by the motor to see if anything loosened up or maybe the cable itself is damaged anywhere. That's where I would start if it just started happening out of nowhere and proceed further as necessary.
I did have A Kawasaki LTD 550 where the clutch cable itself broke inside the black casing it was in between the lever itself and where it went into the motor.

It could indeed . . . i just posted on another thread how vibration loosed my idle mixture screw 4 1/2 turns and spun one of the nuts holding on my right foot peg clean off.

A little strip of threadlock (blue in your case) might help.  It absorbs the vibration.