Some very old web browsersdon’t work well with the Wikimedia wikis. Some old code for browsers that used to be supported is being removed. This could cause issues in those browsers.
IRC recent changes feeds have been moved to a new server. Make sure all tools automatically reconnect to irc.wikimedia.org and not to the name of any specific server. Users should also consider switching to the more modern EventStreams.
When you move a page that many editors have on their watchlist the history can be split. It might also not be possible to move it again for a while. This is because of a job queue problem.
Some translatable pages on Meta could not be edited. This was because of a bug in the translation tool. The new MediaWiki version was delayed because of problems like this.
The new version of MediaWiki will be on test wikis and MediaWiki.org from 30 March. It will be on non-Wikipedia wikis and some Wikipedias from 31 March. It will be on all wikis from 1 April (calendar).