In Resource scheduling app - Operation cannot be scheduled automatically

Hi
One of Work halfway capableness utilization maintained 85%, portion scheduling not capable to execute 100% scheduling of enactment halfway and giving "9XXXXXXXXX/0010: Operation cannot beryllium scheduled automatically"

How to execute 100% scheduling ? owed operations however to docket successful same.

Another enactment halfway adjacent maintained utilization arsenic 85% 110% scheduling achieved, 
Scheduling day are aforesaid successful some lawsuit and capableness Hrs and operating clip are same. 

Please suggest  

Note: We are utilizing S/4 HANA 2021 ,