weird stuff this, I don't envy you trying to track it down. Here's another weird detail I just discovered: When the property labels won't display, they do show up with "fallback values" in another language in the revision history:

Bob Dylan for reference:

any item, but here's an example of an "old" item: https://www.wikidata.org/wiki/Q77413614
This does however apply to newly created items as well as existing ones. It also affects some other properties, like "record label":

weird, it was newly created. Did you purge using the query string or the link in the UI?

started happening again just now:

As for the example above, this now seems fixed!

...this is what I see:

I don't remember which that one was, but here's a fresh example https://www.wikidata.org/wiki/Q48789733

even newly created items have this issue still. Is that part of the deal/a known issue ?

Can you file a bug for this? It might be related to the deployment of caching in SqlEntityInfoBuilder that I did. I will check that.

Fixed on my side, thx!

happens everywhere:

In T230588#5419320, @Lucas_Werkmeister_WMDE wrote:

I think all the items that were updated during the breakage, and were not updated since then, would be broken now – their data was imported using the swapped Ps and Qs, and then after the fix it’s swapped the wrong way. We should be able to get a list of all potentially affected items from recentchanges (Quarry) – @Smalyshev is it possible to tell the updater to re-import those specific entities?

In T229604#5387497, @Ladsgroup wrote:

I'm working on it. It should be back online now with the change I deployed but with missing i18n messages. I'm on it.

affects all pickers - units, dates, language :(

Same bug as reported here: https://phabricator.wikimedia.org/T229604

It looks like the problem is back, stopped working again just now :(

Now fixed on my end 👍

Can confirm: The problem started around 17:45 GMT +1 and affects all browsers (Firefox, Edge, Chrome and variants).

I'd like to add that the same problem also affects property/value suggestions. Started evening/late afternoon May 1. Tested Google, Firefox.