Expected Behavior
Expected Behavior
Clicking Generate should send the prompt to the ComfyUI backend and return generated images.
Actual Behavior
Actual Behavior
With EnablePreviews set to a preview method (e.g. "Enabled (fast latent2rgb)") on a ComfyUI Self-Starting backend, generation requests from the Generate tab hang indefinitely. The request is logged as accepted (backend #0 will load a model: ...), but ComfyUI never receives a got prompt — the request simply never arrives. Eventually it times out with OperationCanceledException at BackendHandler.cs:1386 (LoadHighestPressureNow), and repeated failures can leave the backend queue in a stuck state requiring Interrupt or a full SwarmUI restart.
Notably:
Sending the exact same prompt through the Comfy Workflow tab (direct passthrough) works fine and completes in ~3 seconds.
Setting EnablePreviews to "No Previews" on the backend immediately and reliably fixes the issue — Generate tab requests complete normally afterward.
Steps to Reproduce
None Specific. Installed fresh from start after noticing it in updated swarmui and comfyui. Didn't work.
Debug Logs
Debug Logs
[Info] User local requested 1 image with model 'DreamShaper_8_pruned.safetensors'...
[Debug] [BackendHandler] Backend request #1 for model DreamShaper_8_pruned.safetensors, maxWait=7.00:00:00.
[Debug] [BackendHandler] backend #0 will load a model: D:/.../DreamShaper_8_pruned.safetensors, with 1 requests waiting for 0 seconds
--- (nothing further; no "got prompt" ever appears in ComfyUI's console) ---
(Full log with the resulting OperationCanceledException at BackendHandler.cs:1386 available on request.)
Other
Suspected Cause
The ComfyUI console log shows this on startup:
[ComfyUI-Manager] ComfyUI per-queue preview override detected (PR #11261). Manager's preview method feature is disabled. Use ComfyUI's --preview-method CLI option or 'Settings > Execution > Live preview method'.
This suggests ComfyUI recently changed how preview method is negotiated per-queue-item rather than a global Manager setting. It's likely SwarmUI's EnablePreviews backend option still injects the old-style preview configuration into the prompt payload sent to ComfyUI, which appears to cause ComfyUI to silently reject/drop the request rather than erroring — resulting in a silent hang with no error on either side until SwarmUI's own timeout fires.
Steps to Reproduce
Use a recent ComfyUI build (commit 1377a2f / 2026-07-10, includes PR #11261-related preview changes)
In SwarmUI, set backend EnablePreviews to "Enabled (fast latent2rgb)" (or any non-"No Previews" option)
Generate an image from the Generate tab
Observe: request is queued ([BackendHandler] backend #0 will load a model: ...) but ComfyUI never logs got prompt; eventually times out
Workaround
Set backend EnablePreviews to "No Previews". Live preview can be restored via ComfyUI's own --preview-method CLI arg in ExtraArgs instead of SwarmUI's setting.
System Info
SwarmUI version: 0.9.8.1
ComfyUI commit: 1377a2f (2026-07-10)
OS: Windows 10
GPU: NVIDIA RTX 5060 Ti
Expected Behavior
Expected Behavior
Clicking Generate should send the prompt to the ComfyUI backend and return generated images.
Actual Behavior
Actual Behavior
With EnablePreviews set to a preview method (e.g. "Enabled (fast latent2rgb)") on a ComfyUI Self-Starting backend, generation requests from the Generate tab hang indefinitely. The request is logged as accepted (backend #0 will load a model: ...), but ComfyUI never receives a got prompt — the request simply never arrives. Eventually it times out with OperationCanceledException at BackendHandler.cs:1386 (LoadHighestPressureNow), and repeated failures can leave the backend queue in a stuck state requiring Interrupt or a full SwarmUI restart.
Notably:
Sending the exact same prompt through the Comfy Workflow tab (direct passthrough) works fine and completes in ~3 seconds.
Setting EnablePreviews to "No Previews" on the backend immediately and reliably fixes the issue — Generate tab requests complete normally afterward.
Steps to Reproduce
None Specific. Installed fresh from start after noticing it in updated swarmui and comfyui. Didn't work.
Debug Logs
Debug Logs
[Info] User local requested 1 image with model 'DreamShaper_8_pruned.safetensors'...
[Debug] [BackendHandler] Backend request #1 for model DreamShaper_8_pruned.safetensors, maxWait=7.00:00:00.
[Debug] [BackendHandler] backend #0 will load a model: D:/.../DreamShaper_8_pruned.safetensors, with 1 requests waiting for 0 seconds
--- (nothing further; no "got prompt" ever appears in ComfyUI's console) ---
(Full log with the resulting OperationCanceledException at BackendHandler.cs:1386 available on request.)
Other
Suspected Cause
The ComfyUI console log shows this on startup:
[ComfyUI-Manager] ComfyUI per-queue preview override detected (PR #11261). Manager's preview method feature is disabled. Use ComfyUI's --preview-method CLI option or 'Settings > Execution > Live preview method'.
This suggests ComfyUI recently changed how preview method is negotiated per-queue-item rather than a global Manager setting. It's likely SwarmUI's EnablePreviews backend option still injects the old-style preview configuration into the prompt payload sent to ComfyUI, which appears to cause ComfyUI to silently reject/drop the request rather than erroring — resulting in a silent hang with no error on either side until SwarmUI's own timeout fires.
Steps to Reproduce
Use a recent ComfyUI build (commit 1377a2f / 2026-07-10, includes PR #11261-related preview changes)
In SwarmUI, set backend EnablePreviews to "Enabled (fast latent2rgb)" (or any non-"No Previews" option)
Generate an image from the Generate tab
Observe: request is queued ([BackendHandler] backend #0 will load a model: ...) but ComfyUI never logs got prompt; eventually times out
Workaround
Set backend EnablePreviews to "No Previews". Live preview can be restored via ComfyUI's own --preview-method CLI arg in ExtraArgs instead of SwarmUI's setting.
System Info
SwarmUI version: 0.9.8.1
ComfyUI commit: 1377a2f (2026-07-10)
OS: Windows 10
GPU: NVIDIA RTX 5060 Ti