That is due to the main UI change that Blizzard has documented on the official forums and we have discussed here.
If you install a bug catching addon you will see the errors that are affecting the display.
Basically they have separated the Backdrop system so that any addons that didn't add their own backdrops to their frames will find that there are none and any call to backdrop related functionality will cause errors to occur.
This is one of the forums here that were discussing this when it was first seen.
https://www.wowinterface.com/forums/...light=backdrop