In the New Workfront Experience, the reason you can’t bulk edit Planned Hours for multiple tasks is tied to Duration Type restrictions:
Planned Hours can only be modified for certain Duration Types (for example, Simple). If the selected tasks have mixed or unsupported Duration Types, the field is disabled and shows “multiple values.”
This is a known limitation in the New Experience—unlike the old interface, which allowed direct bulk edits without extra conditions. [experience....adobe.com], [experience....adobe.com]
✅ Workarounds
Check Duration Type
Edit tasks individually or in bulk to ensure they use a Duration Type that supports Planned Hours editing (e.g., Simple).
Once all selected tasks share a compatible Duration Type, the Planned Hours field becomes editable.
Use Workload Balancer or Assignments
Adjust allocations via the Workload Balancer, which can indirectly update Planned Hours for tasks with supported Duration Types. [experience....adobe.com]
Fusion Automation
If you need to update Planned Hours for many tasks at scale, use Workfront Fusion with the Work field (not Planned Hours) in the API. This is the correct system field for Planned Hours updates. [experience....adobe.com]