Warning: Attempt to read property "xxx" on string ... appears in Builder in 1.7.1

Browser: Chrome 111
OS: Windows 10x64
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I have a single post template. I prepopulate it with a post. I add this code element:

<?php
$term_issue_obj = rwmb_meta( 'art_issue' );
$term_issue_name = $term_issue_obj->name;
echo '<button type="button" title="Show TOC">Nummer ' . $term_issue_name . '</button>';
?>

“art_issue” is a MB Advanced Taxonomy field.

This works just fine in v1.7.0. But when I upgrade to v1.7.1, I get this warning in the Builder (it seems still to work in frontend):

Warning: Attempt to read property "name" on string appears in Builder in 1.7.1 ... on line 4

Line 4 refers to the line: “$term_issue_name = $term_issue_obj->name;”

When I rollback, it works again without warning.

Is this a bug? Is this already known? Is there a fix?