[Superman]

It occurs without deleting the previous sketch I import new sketch after first time. Also no features and solid models were modified

Mastercam creates paths relative to selected entities, if you delete any entity that has been used to "construct" a toolpath
.... then that operation technically has been modified but not regenerated
.... this is indicated by the "dirty" icon ( toolpath does NOT match the new parameters of that operation )

so if you delete a sketch, the selected geometry is also deleted ( you should get a screen warning that entities being deleted are used in toolpaths, & you have to acknowledge that warning to continue )
- if you regen a "dirty" path, it should display a warning that the operation contains no geometry.... you would then need to re-select entities before obtaining a toolpath

Are you doing this to keep the same operations to be used on other, different parts ?
- there is an easier way, & you get to keep that part session & toolpath operations for later retrieval