Greetings,
Obvious primary checks would be good electrical power at battery, motor, and cabin, mechanical timing, ignition components,
** and - fuel - ...
If issue started after a recent fill, would suspect impaired fuel filter: if a fleet vehicle, may also want to consider checking for biologic (algae/slime) contamination in the filter and/or tank - if present, use of a bio-side to disinfect the tank may be required:
BIO KLEEN® DIESEL FUEL BIOCIDE: A dual-phase biocide to kill microbes, bacteria and fungus.
Diesel Biocide Additive? - Bob Is The Oil Guy
--
But would recommend to check w/ the Kia Dealer that is closest to your area, if no help from the local garages, locate a local (fleet) service garage, or have the vehicle towed to the dealer for comprehensive diagnostics..
Regards,
GottaCruise