Epic - Process Steps is blank when changed Primary program

Issue Summary

The customer use the Kanban / Process Flow view for portfolio intake. Sudden, near the end of August, many of epics shifted into the far left (unassigned) column of the board, though they had Development Process Steps set.
Audit logs show evidence of when the process step was set, and show that it was never erased

Steps to Reproduce

1. Step 1. Created process flow on Epic level with Program A and Program B
2. Step 2. Created Epic with Primary Program (ART) – Program A and Additional Program – Program B, selected the process step.
3. Step 3. Changed Primary Program (ART) to Program C accidentally which is not associated with the process flow and DO NOT click the save button, and switched back to the original Program A
4. Step 4. Clicks on "Save" or "Save and close".

Reference: Record link - https://loom.com/share/e128061ae9dc419fa65a6dd19020631c

Note: Process step becomes blank when changing the Theme that is not associated with the Primary program / Process flow.

Expected Results

when the primary program is changed, the process step is changed to Select One (blank). The Audit Log doesn't show changes in this scenario.

Actual Results

when the primary program is changed, the process step shouldn’t be erased. The Audit Log should capture the changes.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available