In some cases, content can disappear from Neo blocks when upgrading to Craft 5, due to a field layout element UUID mismatch issue that can occur for older block types. To avoid this issue, the general process you should follow when using the official Craft 5 upgrade guide should be:
- Ensure you are running a version of Neo that provides the
php craft neo/block-types/resave
command- If you have Neo 3, this is at least version 3.10.0
- If you have Neo 4, this is at least version 4.4.0
- Follow the guide up to the step before the first deployment of project config changes to your live environment
- Run
php craft neo/block-types/resave
- Deploy your project config changes and follow the rest of the guide
If you still experience content loss after following the above, please add a comment to Neo issue #943 on GitHub.