I checked the failing limt one and it worked fine. Maybe it was fixed recently?

  ;;; Loading #P"/usr/lib/ecl-21.2.1/sb-bsd-sockets.fas"
  ;;; Loading #P"/usr/lib/ecl-21.2.1/sockets.fas"
  Maxima 5.46.0 https://maxima.sourceforge.io
  using Lisp ECL 21.2.1
  Distributed under the GNU Public License. See the file COPYING.
  Dedicated to the memory of William Schelter.
  The function bug_report() provides bug reporting information.
  (%i1) declare(a,real);
  (%o1)                                done
  (%i2) declare(b,real);
  (%o2)                                done
  (%i3) assume(a>b,b>0);
  (%o3)                           [a > b, b > 0]
  (%i4) limit(log(b-a+%i*eta),eta,0,plus);
  (%o4)                         log(a - b) + %i %pi
  (%i5) limit(log(b-a+%i*eta),eta,0,minus);
  (%o5)                         log(a - b) - %i %pi

Version I've installed is 5.45.1 and gets "log(b - a) + %i %pi" and "log(b - a) - %i %pi", so should be. Gave changelog for 5.46.0 a look but not sure whether it had a direct fix for this or was indirectly fixed due to one of the other closed bugs.

Hmm, there is a weird fix with the limits, could be #484: limit(x=0,x,0) wrong

My university course uses Maxima for optimization modules and essentially none of the examples from the textbook work as they should. Official documentation is sparse and often unhelpful too. The functions output Lisp stacktraces if you do something wrong, rather than actually catching errors and printing some human-friendly message that describes the problem and which particular argument caused it without having to dig into Maxima source code. It would be great CAS software if it was a bit more polished, but unfortunately that is unlikely to ever change - it hasn't in the last 4 years that I've used it at least.