The log says:
Can't locate object method "subfield" via package "<?xml version="1.0" encoding="UTF-8"?><record .. whole xml record" at C4/Search.pm line 1925
1) Set syspref SearchEngine to Elastic
2) go to opac detail and add a tag
3) try to click the added tag
This is the same issue as in 18822 - we assume we got MARC::Record objects from zebra, but in this case we have raw xml fetched from the DB directly.
Possibly in the future we should index the tags and search them using the search engine instead of a direct db call
*** This bug has been marked as a duplicate of bug 18822 ***