When run YAPYMDLCHG on model <model_name> get error
Y2E0028 Escape 40 04/05/18 12:19:09.967751 [email protected] Y2SY *STMT QCMD QSYS 01C8 
From module . . . . . . . . : [email protected] 
From procedure . . . . . . : [email protected] 
Statement . . . . . . . . . : xxxxx
Message . . . . : Previous conversion of Model XXXX not completed 
CAUSE: A previous execution of YAPYMDLCHG for model XXXX failed to complete, 
so model contains work files whose names begin with 'Z'. RECOVERY: (1) 
Determine cause of failure and correct error. Consult customer support if 
uncertain. (2) Restore model from a backup and re-run YAPYMDLCHG command.

Release:
Component: C22E

The Y2E0028 on a model, when converting models using YAPYMDLCHG is typically caused by Z* files in the model library.  Normally there will be just one single Z file 'ZJOBLSTRFP' in the model library.  You will need to delete ALL the Z files from the model library (see the model reference from the joblog), then rerun the YAPYMDLCHG command to resolve the error and convert your model.