I use Paragraph View Mode with Layout Paragraphs.
Layout Paragraphs requires to change the paragraph widget to "layout paragraphs" in paragraphed content types.
After that, when I added Paragraph View Mode, everything went smoothly, I check the box "Enable Paragraph view mode field on this paragraph type".
There is a warning "Behavior plugins are only supported by the EXPERIMENTAL paragraphs widget", but everything worked as expected.
Then I built content.
Then, after I updated modules and upgraded Drupal core to 9.3 , I discovered that I had lost all Paragraph View Mode functionality. The aforementioned checkbox in Paragraph properties was still checked, but no field "Paragraph view mode" was shown anymore, neither in the Paragraph properties' field list, and neither on the paragraph edit window.
Also, all paragraphs were displayed in "default view mode" in the Website's rendered HTML source.
I then tried unchecked the box, saved, then checked it again and saved again, and the functionality was back.
Regrettably, all Paragraph view mode settings for existing paragraphs are lost.
I am not able to exactly pinpoint the problem, but maybe someone will have an idea as to why this happened.
Closed: cannot reproduce
2.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I wasn't able to reproduce the issue unfortunately and don't know what was going on.
It could be reopened or a new issue created once the issue comes back for someone else.
We are now focusing on 3.x version only so I hope it won't happen ever again.