That's a somewhat old version of Cargo, and I think the handling of page data has changed since then. Could you try upgrading to the latest version?

I updated to v3.6.1 now, but still the page categories remain blank after a page edit. When I change this line to "true" instead of "false", it works as expected.

Okay, thanks for trying the update. I have two questions: does the category that you set the page to actually exist, i.e. has a blue link to it? And if you go to Special:CargoTables, does a replacement table row appear for _pageData?

Yes, all categories exist, and no replacement table row appears for _pageData on Special:CargoTables.

That's strange, then - those were my two guesses about what was going wrong. So, I have no idea. I'm glad you found a fix for it, but that particular code change should not be necessary. (And it's not necessary on my wiki.) Barring any further information, I don't know how to proceed on this one. Maybe someone else has some idea...

Change #1249038 had a related patch set uploaded (by TechieNK; author: TechieNK):

[mediawiki/extensions/Cargo@master] Fix missing _categories field data on page save

https://gerrit.wikimedia.org/r/1249038

I have applied this patch to my wiki and, for the first time ever, categorisation works on my wiki! It seems just to be to remove , false from CargoPageData::storeValuesForPage( $title, $useReplacementTable, false );

I have mentioned the problem on the talk page, most recently here: https://www.mediawiki.org/wiki/Extension_talk:Cargo#Storage_of_categories_is_unreliable. It used to be that the following described what happened:

1. - Add categories X and Y.
2. - Cargo immediately knows these categories.
3. - Any edit (including null edit) makes Cargo forget all categories.
4. - Add category Z, in addition to X and Y, in the wikitext.
5. - Cargo immediately knows Z (but only Z, i.e. not X or Y).
6. - The above can be repeated (i.e. Cargo forgetting on edit, and only registering newly added categories).

Now at step 3 Cargo doesn't forget the categories, and at step 5 Cargo knows that the page is in categories X, Y and Z. (By "know" I just mean that it appears on the action=pagevalues page).

MW 1.43.6, Cargo 3.8.6.

P.S. I've removed the patch for now as I don't understand it and for all I know it'll break something else :-)

@Jonathan3 - it's great to hear that this patch works for you!

Change #1249038 merged by jenkins-bot:

[mediawiki/extensions/Cargo@master] Fix missing _categories field data on page save

https://gerrit.wikimedia.org/r/1249038