[REACT] Subtask disappear due to missing event renderer invocation

[chuckn0rris]

Not reproducible in vanilla.

demo-virtualization-bug.zip

Screen.Recording.2025-12-15.at.10.41.13.mov

Forum post

We are encountering a rendering issue with Schedule Pro where a subtask disappears from the timeline after a specific sequence of interactions. The underlying task data remains intact, but the event is no longer rendered, resulting in what appears to be a “phantom” event.

This issue is reproducible using one of the site examples with a few minor adjustments and appears to be related to horizontal virtualization and scrolling interactions.

Environment
• Bryntum Schedule Pro: 6.3.3
• Also reproduced on: 7.0.1
• React: 17.x and 19.0.0

Simplified Reproduction (as shown in video)

As demonstrated in the attached video, the most reliable way to reproduce the issue is:
1. Scroll horizontally so that a subtask is completely scrolled out of view.
2. Continue scrolling into an area with multiple events and dependencies.
3. Scroll back to the original position.

Result:

The subtask is no longer rendered when it re-enters the viewport, even though the underlying data still exists.

Observations / Suspicion

Based on our investigation, it appears that in this scenario the event renderer is not being invoked for the affected subtask when it re-enters the viewport. This suggests a potential issue in the event virtualization or render lifecycle handling.

Notably, this behavior is reproducible in both 6.3.3 and 7.0.1, as well as across React 17 and React 19, indicating that it is not tied to a specific Bryntum or React version.

Impact

From an end-user perspective, this behavior is problematic because tasks appear to be deleted or lost, which causes confusion and reduces trust in the schedule’s accuracy. This issue is currently affecting some of our highest-priority customers, making it particularly important for us to resolve.

Version Constraints / Request

We understand that fixes may be targeted toward newer major versions. However, at this point we are not able to upgrade to v7 due to time constraints and the amount of custom CSS adjustments required on our side. We’ve already done an initial estimation and unfortunately cannot accommodate that work in the near term.

Given that, we wanted to kindly ask:
• If this is confirmed as a bug, would it be possible to apply a fix to the 6.x major version as well?
• Alternatively, is there a recommended workaround or configuration adjustment we could safely apply on our end?

If possible, we would also really appreciate it if this issue could be prioritized, given the impact it has on our top-priority customers.

We’re happy to provide a stripped-down reproduction, additional logs, or assist with further investigation if needed.

Thanks in advance for your time and support.

[chuckn0rris]

Please make a patch for v6 if possible. (read user post)

[mykels]

Hi @matsbryntse, do you have any updates on this? This is quite important for us, as several large customers have been asking for it, as outlined in the forum post. We would really appreciate it if this could be prioritized.

Thank you.

[matsbryntse]

@mykels No updates yet. We'll target to fix this one for an upcoming patch, likely 7.1.1 in January.