Revit Crashing During Synchronize? Resolving UI Freeze Caused by Images in STC Messages

🟢  Current Status
Guardian 3.3.6 is in development and is expected by the end of May 2026. It will include the permanent fix described in this bulletin.

Until then, apply the temporary mitigation in Step 1 of the Resolution section to all affected Project Configurations. This bulletin will be updated when 3.3.6 is released.

Overview

An issue has been identified in Guardian 3.3.5 and prior that can cause Revit to freeze or crash during Synchronize with Central when a Sync Traffic Control (STC) message contains an image.

If Synchronize is initiated before the image fully loads, the UI thread can become blocked, causing Revit to stop responding and eventually crash. Because image loading time may vary depending on system resources, network conditions, or temporary service latency, the issue can appear intermittent and may be difficult to consistently reproduce.

A permanent fix has been implemented in Guardian 3.3.6 to prevent the UI thread from locking during image retrieval.

Symptoms

Users affected by this issue may experience the following behavior:

• STC message with image displayed: A Guardian Sync Traffic Control message or reminder containing an attached image appears after the user initiates Synchronize with Central.
• Synchronize initiated: The user clicks Synchronize with Central while the image is still being retrieved.
• Revit crashes: Revit becomes unresponsive and may crash shortly afterward.

When does this occur?

This issue is intermittent and depends on timing and system conditions at the moment Synchronize is initiated. Factors that may increase the likelihood include:

• Network bandwidth constraints: Slow or unstable network connections
• High system resource load: High CPU or memory usage
• Service latency: Temporary latency on Guardian’s image retrieval
• Timing of Synchronize: Synchronizing before the STC image fully loads

This issue may occur more frequently in constrained environments, while other users may rarely encounter it.

Resolution

These steps must be completed by a Guardian Company or Project Administrator. End users do not have access to Project Configurations and should report this issue to their Guardian Administrator if they encounter it.

Step 1 – Remove images from STC messages temporarily (apply immediately)

Complete the following steps for any affected Project Configuration using images in Sync Traffic Control messages.

For each affected project:

1. Navigate to the affected model’s Project Configuration.
2. Under Custom Interactions, navigate to Enable Sync Traffic Control and select the ⚙️ settings icon.‍
3. Locate the Protection Mode row, select Edit message and remove any images from the message body. Select OK to save the message.
4. Locate the Remind users to synchronize after row, select Edit message and remove any images from the message body. Select OK to save the message.
5. Select OK to save the Project Configuration.
6. If users have the affected model open in Revit when the Project Configuration is updated, they must restart Revit for the change to take effect.

Step 2 — Deploy Guardian 3.3.6 once available (permanent fix)

Guardian 3.3.6 is the permanent resolution and is expected by the end of May 2026. This release modifies how image loading is handled to prevent the UI thread from blocking, regardless of system load, network conditions, or image retrieval timing. Once available:

1. Deploy Guardian 3.3.6 to all affected workstations.
2. Once 3.3.6 is confirmed installed across your environment, images can be restored to STC messages.

⚠️  Important
Do not restore images to STC messages until Guardian 3.3.6 has been fully deployed to all workstations. Re-adding images while earlier versions remain in use will reintroduce the risk of crashes.

Further Assistance

If you have followed these steps and Revit continues to crash during Synchronize, please contact our support team.