Keeping your Internet browser up-to-date is important for both security and ensuring that web pages load properly.
Optionally with those error messages: This is caused by a change in PCRE 8.34.
You need to update Media Wiki to a supported version.
A: Major version updates to the stable channel of Google Chrome tend to happen about every six weeks, although security fixes can come at any time.
See Release Early, Release Often for more information.
By default, it is set to use Image Magick for conversion. Ensure that your $wg Image Magick Convert Command variable is valid.