OK, I did not have Layouts enabled.
And with Layouts active, the issue is replicable.
It is confusing that in the package I received, there was no Layouts included - but however, when I activate it (which I should, I do not know why I missed it), I can replicate the issue when I fill all field.
When I fill all field but not the last set of checkboxes I can submit as well (I mean, with a successful redirect).
==> Note that in the Layout, that designs the page with the form, I change the Visual Editor to show only the title, and added a Post Content cell instead.
That is designated to show the content of the post as you have the Form as a ShortCode in that page's content.
So the problem is with all the fields, AND the last section.
If you leave out that section the redirect works.
Now, when you select the Check boxes at the end, all of them, then you get these errors when you submit (note, I also have added some values to the other fields, as usual - but this time as well selected all the checkboxes)
( ! ) Warning: trim() expects parameter 1 to be string, array given in .../wp-includes/class-wp-query.php on line 736
( ! ) Warning: strip_tags() expects parameter 1 to be string, array given in .../wp-includes/formatting.php on line 1981
Redirect fails.
So, the form could not complete, that is the issue that blocks the redirect, it is the PHP error above.
I have seen this in past, it was due to several fields, taxonomies, form and layout displaying it all:
https://toolset.com/forums/topic/cant-select-multiple-taxonomies-and-regular-checkboxes/
The exact issue we see here if you ask me.
In fact none of the taxonomies get saved as far I see.
And that would match this issue:
"Checkbox Field(s)" AND "A Custom Hierarchical Taxonomy displayed as Checkboxes" within a Toolset Edit Form, displayed via a Content Template used in a Layout, is failing.
That is quite much what we see here.
But this should be solved since Toolset CRED 1.9.1 and Layouts 2.0.2
Now, I have your duplicate locally where I can see the issue and probably already pointed the issue.
I just need to figure out, if that as well happens on a fresh install - then it is a regression
This will require me a little time and I will feedback here tomorrow the results.
In case I cannot replicate it, I will in any case work on the duplicate with the new data and steps, which now are clear and simple to replicate the problem
Then we can also find a solution.
For now, I see the only solution is to either remove all, or eventually just restrict the number of, taxonomies in that form.
That should solve the issue, but of course, you will not have the taxonomy fields in the form, this is hence only a workaround for now.