We are encountering a significant problem with APB, rendering it unusable. Although APB was scheduling and sequencing correctly. Now a portion of the shop orders become unscheduled during the process of scheduling, also from the same part number and thus setup (standard operations and routing template). However, the operations don't have the Scheduling Status ‘Unscheduled’. We have thoroughly examined all aspects of routing, work centers, labor classes, tools, and calendars, but we have been unable to identify the cause of this issue.

The screenshot below exists out of two shop orders. SO 528409 is scheduled fine. SO 524934 isn't scheduled properly and the operations don’t have a start date from step 620 onwards. It seems to happen randomly at different operation steps.