Since Bug 30578 the previous auto completion (circ/ysearch.pl) was replaced with the jQuery autocomplete functionality. The search on the advanced order search page in acquisitions still sends "term" as query parameter, but it is now received by api/v1/patrons instead of circ/ysearch.pl and that api route does not recognise this parameter name. I do not understand how the two autocomplete features work, or what has to be done to fix this, so I'm unable to provide a patch for it.
Hi Stefan, I believe this was fixed by bug 31782 now. *** This bug has been marked as a duplicate of bug 31782 ***