Modal view with fewer than 100 blocks fails to render, no error in logs

[ShivamS136]

Description

According to the Slack documentation, a modal view can contain up to 100 blocks. However, in my multi-step form workflow, when the step 2 view contains a number of blocks well within this limit (e.g., 20 blocks at the top level), the view fails to render. There are no errors in the logs, and the view that is supposed to be rendered works perfectly in the Block Kit Builder. Despite this, the modal is not updated and instead displays the error:

"We had some trouble connecting. Try again?"

This makes it difficult to debug or understand what is causing the issue.

---

Version

slack v3.4.0

---

OS Info

ProductName:    macOS
ProductVersion: 15.5
BuildVersion:   24F74
Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:29 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6030

---

Steps to Reproduce

1. Create a multi-step modal workflow.
2. In step 2, define a view with a number of blocks (e.g., 20) at the top level, well below the 100 block limit.
3. Push or update the modal to display step 2.
4. Observe that the modal fails to update and shows the error:
   "We had some trouble connecting. Try again?"
5. Note that there are no errors in the logs, and the view renders fine in Block Kit Builder.

---

Expected Result

• The modal should update and render the step 2 view as defined, since the number of blocks is well within the documented limit.

---

Actual Result

• The modal fails to update and displays an error.
• No errors are logged.
• The view is valid and renders in Block Kit Builder.

---

Questions

1. Block Limit Scope:
   When a modal view is pushed (using response_action: "push") instead of updated, is the 100 block limit applied only to the step 2 view, or to the combined blocks of both step 1 and step 2 views?

2. Block Limit Definition:
   Does the 100 block limit apply only to top-level block elements, or does it also count nested elements (e.g., elements inside rich_text or input blocks)?

3. Error Handling:
   Is there a handler or callback function that can be attached to a Slack Function to catch errors that occur during the submission handler? In this case, the view is being created and returned from the addViewSubmissionHandler without any error, but the modal fails to update and no error is surfaced. How can such issues be detected or debugged? addUnhandledEventHandler is also not able to catch the issue here.

---

Requirements

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

[hello-ashleyintech]

hi, @ShivamS136! Thanks for submitting this question.

Block Limit Scope:

When a modal view is pushed (using response_action: "push") instead of updated, is the 100 block limit applied only to the step 2 view, or to the combined blocks of both step 1 and step 2 views?

I believe it counts on what modal view is being surfaced at a time, so the 100 block limit should apply to step 1 and step 2 views.

Block Limit Definition:

Does the 100 block limit apply only to top-level block elements, or does it also count nested elements (e.g., elements inside rich_text or input blocks)?

For this one, I believe any blocks will count, nested or not. It sounds like your modals are falling within this limit, so they should render as expected as this limit would not apply.

Error Handling:

Is there a handler or callback function that can be attached to a Slack Function to catch errors that occur during the submission handler? In this case, the view is being created and returned from the addViewSubmissionHandler without any error, but the modal fails to update and no error is surfaced. How can such issues be detected or debugged? addUnhandledEventHandler is also not able to catch the issue here.

As of right now, we do not currently have anything like this - you could add some console.log() statements in your view submission handler to narrow down specific lines in the code where it may fail. Feel free to raise interest for more robust logging here.

Could you send the code for how you're handling the first modal and pushing the second modal view? This may help me figure out why you're getting this error as well.

[ShivamS136]

Thanks for the reply.

I believe it counts on what modal view is being surfaced at a time, so the 100 block limit should apply to step 1 and step 2 views.

The limit should apply to both steps separately or combined? Like, if I am pushing step 2 view, then the limit will be applied to the block elements in step 2 or both steps? Same for "update" as well?

For this one, I believe any blocks will count, nested or not. It sounds like your modals are falling within this limit, so they should render as expected as this limit would not apply.

That seems to be very hard limit because if I am setting initial value of rich text input, or having dropdown then it will take lot of block element space.

For logging, I am getting logs upto before the return statement from addViewSubmissionHandler function but nothing after that. So not sure if the return value was accepted or not or resulted into error. How can I add logs for that?

And I also tried debugging mode today but no luck in setting that up.

For code, I'll try to create a sandbox and share here.