"Required input is missing" error in delegate-only mode

[elson]

When running a workflow in "delegate-only" mode and passing a String primitive to a Save Image node, the workflow fails with an Required input is missing: filename_prefix error and the image is not saved.

Error Details

• Node ID: N/A
• Node Type: N/A
• Exception Type: Prompt execution failed
• Exception Message: TypeError: can't access property "node_errors", c is null

System Information

• ComfyUI Version: 0.22.0
• Arguments: main.py --listen 0.0.0.0 --port 8088 --enable-cors-header --cpu --enable-manager
• OS: linux
• Python Version: 3.12.13 (main, May 19 2026, 23:48:44) [GCC 14.2.0]
• Embedded Python: false
• PyTorch Version: 2.12.0+cu130

Devices

• Name: cpu
  • Type: cpu
  • VRAM Total: 33519362048
  • VRAM Free: 20988223488
  • Torch VRAM Total: 33519362048
  • Torch VRAM Free: 20988223488

Master Logs

[Distributed] [Distributed][exec:exec_1780043900385_0f1f1e] Orchestration start: requested_workers=1, requested_ids=['7d3168a8-2f87-4a0e-8de9-d1296a166ac9'], websocket=True, probe_concurrency=8, prep_concurrency=4, media_sync_concurrency=2, media_sync_timeout=120.0s, load_balance=False
[Distributed] [Distributed][exec:exec_1780043900385_0f1f1e] Probing 1 workers with probe_concurrency=8
[Distributed] [Distributed][exec:exec_1780043900385_0f1f1e] Worker probe complete: active=1/1
[Distributed] Removed upstream reference 'images' from node 11 for delegate-only master prompt.
[Distributed] Removed upstream reference 'filename_prefix' from node 9 for delegate-only master prompt.
[Distributed] Inserted placeholder node 16 for collector 11 in delegate-only master prompt.
[Distributed] [Distributed][exec:exec_1780043900385_0f1f1e] Active distributed workers: Modal (7d3168a8-2f87-4a0e-8de9-d1296a166ac9)
Failed to validate prompt for output 9:
* (prompt):
  - Required input is missing: filename_prefix
* SaveImage 9:
  - Required input is missing: filename_prefix
Output will be ignored
[Distributed] API Error [500]: Invalid prompt: {'type': 'prompt_outputs_failed_validation', 'message': 'Prompt outputs failed validation', 'details': 'Required input is missing: filename_prefix', 'extra_info': {}, 'node_errors': {'9': {'errors': [{'type': 'required_input_missing', 'message': 'Required input is missing', 'details': 'filename_prefix', 'extra_info': {'input_name': 'filename_prefix'}}], 'dependent_outputs': ['9'], 'class_type': 'SaveImage'}}}
[Distributed] job_complete received canonical envelope - job_id: exec_1780043901365_55ef5f_11, worker: 7d3168a8-2f87-4a0e-8de9-d1296a166ac9, batch_idx: 0, is_last: True, queue_size: 1

Cloud Worker Logs

Model SDXL prepared for dynamic VRAM loading. 4897MB Staged. 0 patches attached.
100%|██████████| 20/20 [00:02<00:00,  8.25it/s]
100%|██████████| 20/20 [00:02<00:00,  8.39it/s]
Model AutoencoderKL prepared for dynamic VRAM loading. 159MB Staged. 0 patches attached.
Prompt executed in 3.51 seconds

Workflow

input_bug.json

[elson]

Here is a further example of removed inputs failing in delegate-only mode, this time for a switch node 🙏

Master Logs

Distributed] [Distributed][exec:exec_1780048454643_54e3b8] Orchestration start: requested_workers=1, requested_ids=['7d3168a8-2f87-4a0e-8de9-d1296a166ac9'], websocket=True, probe_concurrency=8, prep_concurrency=4, media_sync_concurrency=2, media_sync_timeout=120.0s, load_balance=False
[Distributed] [Distributed][exec:exec_1780048454643_54e3b8] Probing 1 workers with probe_concurrency=8
[Distributed] [Distributed][exec:exec_1780048454643_54e3b8] Worker probe complete: active=1/1
[Distributed] Removed upstream reference 'images' from node 854 for delegate-only master prompt.
[Distributed] Removed upstream reference 'on_false' from node 850 for delegate-only master prompt.
[Distributed] Inserted placeholder node 869 for collector 854 in delegate-only master prompt.
[Distributed] [Distributed][exec:exec_1780048454643_54e3b8] Active distributed workers: Modal (7d3168a8-2f87-4a0e-8de9-d1296a166ac9)
[Distributed] [Distributed][exec:exec_1780048454643_54e3b8] Media sync for worker 7d3168a8-2f87-4a0e-8de9-d1296a166ac9: uploaded=0, skipped=1, missing=0, referenced=1
Failed to validate prompt for output 851:
* ComfySwitchNode 850:
  - Required input is missing: on_false
Output will be ignored
[Distributed] API Error [500]: Invalid prompt: {'type': 'prompt_outputs_failed_validation', 'message': 'Prompt outputs failed validation', 'details': 'ComfySwitchNode#850: Required input is missing (on_false)', 'extra_info': {}, 'node_errors': {'850': {'errors': [{'type': 'required_input_missing', 'message': 'Required input is missing', 'details': 'on_false', 'extra_info': {'input_name': 'on_false'}}], 'dependent_outputs': ['851'], 'class_type': 'ComfySwitchNode'}}}
[Distributed] job_complete received canonical envelope - job_id: exec_1780048456325_3a4106_854, worker: 7d3168a8-2f87-4a0e-8de9-d1296a166ac9, batch_idx: 0, is_last: True, queue_size: 1

Workflow

input_bug2.json

[robertvoy]

Hi @elson — I opened a candidate fix in PR #86: #86

Could you please test branch fix/issue-85-delegate-master-primitives against your attached workflow and confirm whether it fixes the Required input is missing: filename_prefix error?

Suggested test steps:

cd ComfyUI/custom_nodes/ComfyUI-Distributed
git fetch origin
git checkout fix/issue-85-delegate-master-primitives
# restart ComfyUI, then rerun the issue #85 workflow

The change preserves lightweight primitive inputs, specifically PrimitiveString -> SaveImage.filename_prefix, in delegate-only master prompts while still pruning heavy upstream nodes.

I will keep the PR unmerged until you confirm the workflow saves correctly.

[elson]

Thanks @robertvoy! That works for the PrimitiveString case 👍

Still same behaviour for the second switch node example, but I think that is expected given the scope of your change. Any suggestions on how to handle or workaround that type of workflow configuration?

[robertvoy]

Thanks @elson — I missed the second workflow in the thread initially. I have updated PR #86 to cover that switch-node case too.

What changed in the latest branch update:

• Keeps PrimitiveString -> SaveImage.filename_prefix for the original case.
• Also keeps LoadImage -> ComfySwitchNode.on_false for the second workflow, so on_false is no longer pruned from the delegate-only master prompt.
• Still prunes heavyweight upstream compute nodes and keeps the collector placeholder behavior.

Validated on the 5090 ComfyUI_dev environment:

• tests/test_prompt_transform.py: 55 passed
• Full suite: 236 passed

Could you please fetch the updated branch and retest input_bug2.json?

cd ComfyUI/custom_nodes/ComfyUI-Distributed
git fetch origin
git checkout fix/issue-85-delegate-master-primitives
git pull
# restart ComfyUI, then rerun input_bug2.json

Latest commit: 45d08ce76df5ef09c63a553b27f756fd8a854045