Is the issue tags published from WordPress just with a single topic, or are you not able to get tags to display for any topics? Do you have the
suppress overlapping tags in list site setting enabled on Discourse? If so, is there a chance that this is preventing the tags from being shown?
If you are unable to get tags published from WordPress to work at all, can you let me know which WordPress editor you are using? Is the problem happening with posts published with the Block editor, or with posts published with the Classic editor?