Field automatically converted from Neo to Matrix on upgrade to CraftCMS v5

[sadanyagci]

Bug Description

Since upgrading to CraftCMS version 5, my most complex Neo field was somehow automatically converted into a matrix field. Its subfields and such are all pulled out as their own fields. This has created a mess that is very difficult to work with and that I never wanted.

It looks like I can't simply change the field back from a matrix field to a Neo field, as none of its subfields change with it. How can I bring back its original Neo structure without compromising any of my website data? The entire website is literally built on this field. I need it to be a Neo field again. Strangely, my other Neo field didn't change into a matrix field during the upgrade. Just this one.

Steps to reproduce

Upgrade from Craft Pro 4 to Craft Pro 5.5.6.1 with Neo 5.2.19

Expected behaviour

Neo fields should remain Neo fields.

Neo version

5.2.19

Craft CMS version

Craft Pro 5.5.6.1

What is the affected Neo field's propagation method?

No response

Does this issue involve templating, and if so, is eager-loading used?

This is not a templating issue

[ttempleton]

I did not experience this on a few Craft 5 upgrades that I performed with the latest Craft and Neo versions yesterday. I'm also unsure how it is possible for Neo to have done this, since the only times Neo performs a conversion to Matrix are when a controller action is called by a button press on the Neo field settings page, or when Neo is uninstalled.

By any chance was the field originally built as a Matrix field before being rebuilt as a Neo field? Just wondering if there is anything left in either the project config or the database related to a Matrix field that might be causing issues. I'll recommend restoring the Craft 4 version of the website, checking for any issues related to that, and reattempting the Craft 5 upgrade.