The task [Open] [Feature] T65459 Allow configuration of the Minerva menu was already resolved by Extension:MinervaMenu that worked like charm until MW 1.39 when the hook MobileMenu was depreciated. The task can be resolved again by updating the orphaned extension MinervaMenu in line with the current hooks.

Close it. Sorry about the late response. The migration from 1.38-4 to 1.39 was delayed longer than expected.

@lucamauri That is a definitely blocker for me, blocking any upgrade from 1.38, regardless if it is caused by 1.39 or LabeledSectionTransclusion extension. This functionality is used on high number of pages for me and is essential.

Yes, there is a node #prp-pages-output, the contents is <div class="prp-pages-output" lang="en">
<p><span>
<span class="pagenum ws-pagenum" id="1" data-page-number="1" data-page-name="Page:File name.pdf/1" data-page-index="1" data-page-quality="4" title="File name.pdf/1">
<span id="pageindex_1" class="pagenum-inner ws-noexport">&#8203;</span>
</span>
</span><br />&#32;</p>
</div>

Thanks. To add more information. The pages that showed the error message "There was an issue displaying this preview" now show the preview. No edit, not even null edit was done. Just the server was running. (yes, the pages with {{TOCright}} and section pointer). Freshly updated existing pages that used to have preview suddenly do not have one. I will wait a day again to see if the previews for those pages appear. I suspect there may be some caching somewhere that may cause the issue. The whole problem became noticeable after upgrade from 1.37.1 to 1.38.2 when everything was refreshed, server rebooted and cache is cold but with no error message anywhere I have no chance of tracing it.

Retests: all passed. Thanks.
a) OK.
MediaWiki 1.27.1
PHP 7.0.14 (apache2handler)
MariaDB 10.1.22-MariaDB
ICU 58.1

Wikitext:
<graphviz border='frame' format='png' caption='Teacher - pupil'>
digraph Teacher_pupils {teacher->pupil1; teacher->pupil2; teacher->pupil3; teacher->pupil4; t->p;}
</graphviz>

Retested MW 1.27.1 - OK, works like a charm. Not a trace in Recent changes except the changed page.

Unfortunately, retest on both 1.28 and 1.27 gives the same result
... includes/upload/UploadBase.php: Call to undefined method UploadLocalFile::getName()
on line 395 for 1.28 and line 386 for 1.27.

I may be late with the idea; it might be useful to check the extension:Score. It has a very similar work flow: it takes as an input metalanguage (lilypond or abc), it processes the input by using the external packages (lilypond/abc) and displays the image created by them. On top of that it creates the page property (suits me a lot) score for a page using the lilypond/abc.

I am afraid not much. This is a design problem, not a traceable bug, setting $wgShowExceptionDetails = true;
$wgShowDBErrorBacktrace = true; does not produce anything. Until Welterkj finds time for it or somebody else with deep knowledge of extension programming (I am not the one) who has time and is allowed to produce fix by the developer, we are stuck. It is the only extension that produces kind of relations between entities I need so I installed, tested, rejoiced and disabled (unfortunately such polution of recent changes and categories is not acceptable). On top of that under MW 1.28 this extension is a victim of Incompatibility with AbuseFilter and SpamBlackList extensions (see Extension_talk:GraphViz)

It is not one message, but a string of them, captured them all (produced during the load of the Main Page):
Warning: Parameter 1 to wfTimelineExtension() expected to be a reference, value given in includes/Hooks.php on line 195