The client patch 2.4.2 was released today. Along with it came problems with popular addons like Cartographer, Auctioneer and others. Although a patched version of Auctioneer has been released already, it is to be expected that many addons are still broken and need to be updated.
Please make sure to check your addons for updates or temporarily disable the broken ones to minimize gameplay issues.

As usual, the latest patchnotes can be found here.