To record a frame rate such as 23.98 fps from within 59.94 fps, VFR should be selected for the Record Type. If Normal, as opposed to VFR is selected, the Ki Pro Mini will produce the standard 59.94 fps. You can determine if the Ki Pro Mini is actually seeing 23.98 (24) by entering STATUS.
If you need further assistance, contact AJA Technical Support via phone or email Monday through Friday, PST.
I am not familiar with that camea but In addition to what Aja said ( kipro in VFR mode) double check and make sure that the userbits are in fact turned on set to tcg mode. On some Panasonic models, this is not turned on by default and you have to physically turn this feature on via the menus. Perhaps it’s the same for JVCs.