Ever since updating to the latest version of IPB, I can no longer see the backgrounds of any of my installed themes (that have been updated to the latest version too).

Is this a bug affecting anyone else or is there something wrong with my board?

There was a bug in version 4.1.10 that was fixed in 4.1.11 (released today).

Are you using 4.1.11? If not, just upgrade to that version and you should be good.

If the problem remains after being on 4.1.11, please file a ticket to support, and we'll be glad to assist.