@Rical: Steps to reproduce welcome, see https://mediawiki.org/wiki/How_to_report_a_bug - thanks!

I guess this was about https://fr.wikisource.org/wiki/Sp%C3%A9cial:Version ?

When I recorded the bug T122752, I was not able to say when it appeared. Then I included in my code

if mw.site.currentVersion == "1.29.0-wmf.8 (a60b7fe)"

and a display of a red error each time the version change, each 5 - 10 minutes when I try my code.
In local I also record Special:version of all previous versions from 2016-06-19:
20170119-23:36 : Mediawiki-Wikisource 1.29.0-wmf.8 (rMWa60b7fe6f5e9)UTC-20170117-21:39.html
20170108-19:38 : Mediawiki-Wikisource 1.29.0-wmf.7 (rMWca362d6df08b)UTC-20170106-14:47.html
20170105-21:33 : Mediawiki-Wikisource 1.29.0-wmf.7 (rMW8f47c69aed05)UTC-20170105-15:11.html

We could imagine a new test case for jenkins-bot which checks the version in Mediawiki:Version and compares it with the previous one.
For 1.29.0-wmf.7 (rMW8f47c69aed05) : 1, 29, 0, and 7 follow digital coherent cycles and in parentheses 7 new alphanumeric chars.

Another change in the https://fr.wikisource.org/wiki/Spécial:Version display:

• Special:Version = 1.29.0-wmf.18 (rMW9ab639f85dc6) at UTC-20170403-15:20
• Special:Version = 1.29/wmf.19 (rMWe4784c6b8dd6) at UTC-20170407-20:52

I observed on my wikis that the SHAs were sometimes missing. In my case it was because I use to run git gc, and during this operation the references are packed together in the file .git/packed-refs and MediaWiki didn’t read this file. I proposed a patch in T155747 to implement this feature (rMW125f832) and it was merged and deployed on Wikimedia some days ago.

I’m not sure if the issue you observed was caused by a git gc, anyway could you observe in the following days/weeks if there is still the issue, and close it if it does no more happen (it can always be reopened if it reappears later).

@Seb35: From 2016-06-19, I look at mw version number each day or about.
The last non standard was "MediaWiki_1.29/wmf.19" on 2017-04-07.

I am very far to know if .git/packed-refs can or not insure a better stability on the display of this version number.

in the https://fr.wikisource.org/wiki/Spécial:Version
At the same UTC time : 2018-01-12T07:43:00 there two different values:

• from Special:Version = 1.31.0-wmf.15 (rMW09537008d55f)
• from Central module = 1.31.0-wmf.16 (rMWa31d45c80eef)

I try to fast form a dedicated test.

The test is in https://fr.wikisource.org/wiki/Utilisateur:Rical/MediawikiVersion
But the bug has already disappeared.
Sorry for this time. This is ready for next cases.

I don't see a bug, but different results of caching. Plus these last comments sound unrelated to the actual topic of this task.