1. So perhaps is an issue with custom post types, which were created in the old version of Types?
That should not be an issue, those Fields are populated by CRED, not Types.
Also, an update should not cause this, after all, we updated the Plugins as well on the Discover-WP instances.
2. my CRED notifications worked fine, before I updated all my Toolset Plugins. And after the updates, they didn't work without the ID on two of my client sites.
This seems a corruption of the Database.
I am not sure anymore, have you tried to re-create a Form?
Often those issues are solved by it.
Also, of course debug steps like not using any other Plugin but Toolset and a native Theme will show more, but I believe we did that already, right?
3. Am I right, that the types-field doesn't combine the given string with the database, but instead with the string in the dropdown-field.
I am not sure what you mean here.
4. But this would only check, if the dropdown is not "1 child", not if there are more children because I can't check with "gte" in a text-field.
What are you using, Select or Tex Fields?
These are not the same, they got nothing to do with each other.
A Text Field will hold a String you need to compare to.
Let's say your Field (Text Field) holds the value "my-value", so that is what you compare it to.
If it's a Select Field, the value to compare is what you set it to save in Toolset > Post Fields > your_filed_group > Edit > your_field > Custom field content.
Natively in Select Fields, those are numeric values, one each option, increasing, which results in values like 1,2,3 etc.
When you compare a Select Field in a Conditional you need to tell the code what you want to compare (Display value or Stored value?).
So the condition in the case of a Select Field would look something like this:
[wpv-conditional if="( '[types field='select' output='raw' id='%%POST_ID%%'][/types]' eq '1' )"]
conditional shown content here
[/wpv-conditional]
(already adapted to your specific situation where you need %%POST_ID%%)
This would compare if the Field's selected option is "1".
If you want to check if it is selected at all (not empty) you need to make sure that in Toolset > Post Fields > your_filed_group > Edit > your_field > Custom field content there is NO default selected, as otherwise, the Post will save something in all cases.
As long there is no default and the user selects NOTHING when saving the post, the condition to check whether it's empty or not would be:
[wpv-conditional if="( '[types field='select' output='raw' id='%%POST_ID%%'][/types]' eq '' )"]
conditional shown content here
[/wpv-conditional]
As you see I also add the attribute "raw" to make sure we compare only values and no HTML.
Does that solve the problems?