This issue is influencing the results displayed on the snyc pages of the mix'n'match catalogues e.g. https://tools.wmflabs.org/mix-n-match/#/sync/745 where I detected the error first
Thu, Aug 15
Wed, Aug 14
Wed, Jul 31
Concerning the duplicates mentionned in T229391: Two wikidata items with the same sitelink.
A few more examples of double creations in wikidata which where done without that I intended to do so:
May 16 2019
And here are another 3 examples where creating wikidata items on base of categories on Commons lead to the creation of 2 items on wikidata linked to the same pages on Commons and on en-wikipedia
May 15 2019
Today there was again on 7 occassions unintended creation of duplicate items in wikidata:
Apr 25 2019
Today there was again twice a creation of duplicate items in wikidata:
Jan 17 2019
The list of more examples and a description of how such duplicates were generated unintentionally is now availyble on: https://www.wikidata.org/wiki/Wikidata:Project_chat/Archive/2018/10#Items_created_unintentionally_twice_on_several_occasions
After removing the local interwiki on https://commons.wikimedia.org/wiki/Category:Yema_T80 i manage again to reproduce the error as well on thi spage and get the simular error message:
I just retried as well for the second exemple and got a similar error in tmy browser (Firefox Version 64.0.2, 64 bit) webconsole:
Jan 16 2019
Another exemple for the same behaviour are https://commons.wikimedia.org/wiki/Category:1893_in_Wyoming and https://en.wikipedia.org/wiki/Category:1893_in_Wyoming
Oct 26 2018
Oct 25 2018
This seems to be independent of the browser used as I get the same behaviour with Microsoft EdgeHTML 17.17134
Oct 24 2018
Oct 15 2018
There are more examples and a description of how such duplicates were generated unintentionally https://www.wikidata.org/wiki/Wikidata:Project_chat#Items_created_unintentionally_twice_on_several_occasions
Jul 20 2018
Nov 17 2017
By now this issue is solved (at least from what I noticed) Aadding links to other languages is again working at least from both Commons and en.wikipedia.
Nov 16 2017
The same issue happens as well on Commons. I went on https://commons.wikimedia.org/wiki/Category:1_Princes_Dock clicked there on the left hand menu under In Wikipedida on 'Add links' and get the error message "An unknown error"occurred".
Nov 29 2016
After making some more tests today everything is back to normal as well with firefox 52 : 52.0a2 (2016-11-28) (32-bit)
Nov 28 2016
I now noticed that everything seems working correctly with Firefox 50.0 while i noticed the issue with Firefox 52.0 a2 (Aurora) I hope more testing will help clarifying the issue.
The same issue reappeared today!
Nov 10 2016
many thanks to all those who helped solving this issue!
I notice the same issue again.
By now (some minutes later) everything is back to normal. So most probably it was just due to some issues on the wikidata servers.
ups I mistaked in the date I noticed it today 10 november 2016 and everything worked well yesterday evening 9 november 2016.
Sep 18 2016
Dec 21 2015
Jan 10 2015
Ups my last sentence in the previous comment is not correct It should be:
I just noticed the following error message concerning network (using function Inspect Element of Firefox) the following:
I get the same error for days on any message groupe I try to load the list of messages to translate: