Error saving BlockList content – "'T' is an invalid start of a value" in Umbraco 15.2.3

Questions
1

Hello,

I’m experiencing an issue with a BlockList property on a content node that uses a custom Accordion component. Here’s the context:

  • I initially set up the project using Umbraco 15.2.2 (the latest version at that time). The Accordion component is implemented as a BlockList element (Cd_Cb_Accordion) that contains multiple category blocks (Cd_Cbi_AccordionCategory), each with nested items (Cd_Cbi_AccordionItem).
  • The ModelsBuilder-generated models are used for strong typing.
  • On first creation, everything works as expected. However, when I try to save or republish the content (even without making any changes), I get the error:
"T is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0."

I suspected this might be an issue with the version, so I updated to Umbraco 15.2.3, but the error persists.

The stack trace indicates that the error occurs during JSON deserialization within the BlockEditorDataConverter (using System.Text.Json). It seems the problem arises when merging or cleaning the BlockList property value during a save.

Has anyone encountered this behavior? Any insights into whether this might be caused by a type mismatch or a serialization issue with the BlockList JSON structure would be greatly appreciated.

Thanks,
Olti

2

Ah it looks like this is the same issue as this other thread:

It will be fixed for 15.3,

The 2nd release candidate of 15.3 just came out today, would be worth giving it a try:

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3

Thank you! I’ll give it a try. Otherwise, I might wait until March 20th since it’s a live production project.

4

Oh cool, live already! I would recommend doing some testing on RC2 so that you know you can upgrade when the time comes and if anything is still broken, it will greatly help us fix bugs before then :folded_hands:

5

Thank you for pointing me to the 15.3.0-rc2 release! I tested it, and I can confirm that the BlockList serialization issue has been resolved. However, I’ve noticed a few other things that might still need attention:

  1. Missing loading indicator on save & publish
  • When saving or publishing a content node, there is no loading spinner on the buttons. This makes it unclear whether the action is in progress.
  • In previous versions (e.g., Umbraco 13), the UI would disable interactions during the process and display a loading indicator. Currently, the interface remains fully interactive while saving/publishing, which might lead to unintended changes before the operation completes.
  1. Block List item selection UX
  • When selecting a block in the Block List editor, the clickable area is still limited to the lower section where the block’s name is displayed.
  • Ideally, the entire block container should be clickable to improve usability.
  1. Initial “Not Found” error in Content section
  • When navigating to the Content section, I briefly see the message:
    “Not found, The requested route could not be found. Please check the URL and try again.”
  • After a few seconds, the content loads correctly.
  • In previous versions, a loading indicator would appear instead of an error message, which provided a better user experience. The error message should ideally only appear when the page truly cannot be found, not while the content is still loading.

Just wanted to share these observations in case they are unintended behaviors. Let me know if you need any additional details!

Thanks again for your help!

6

Glad to hear it’s working again!

Are these new issues after you upgraded? If these are new issues not present in 15.2 we really need to know about them on the issue tracker ASAP:

7

No, these issues were also present in 15.2.3. I had hoped they would be resolved in 15.3, which is why I mentioned them now.

I did see the issue regarding the Block List selection behavior (where only the lower part of the block is clickable) in the issue tracker, but I’m not sure if the other points are already reported.

That said, I haven’t noticed anything breaking due to the upgrade from 15.2.3 to 15.3.0-rc2—everything seems to be functioning the same as before, apart from these UI-related concerns.

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8

Good to know! Make sure to create issues if they don’t exist yet, the team is working from the list on the issue tracker.

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9

Okay, I’ll create issues for the two items I couldn’t find in the issue tracker. They might already exist, but I don’t have much time to go through everything in detail. So, I’ll submit them, and if they are duplicates, they can simply be ignored.

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10

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