Forum - SQL bug

When clicking the "View your post" (https://wyday.com/forum/search.php?search_id=egosearch) link, the following error occurs:

General ErrorSQL ERROR [ mysqli ]

Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'forum.p.post_id' which is not functionally dependent on columns in GROUP BY clause;...

The forum software we're currently using (phpBB) is being replaced later this year with open source forum software that actually works well on modern infrastructure.

phpBB is being held together with duct-tape and twine. Lots of things are falling apart, but it's just barely useful enough to keep together until we move to our new forum software.