What did you do to get this?

Please check this fix: https://github.com/b2evolution/b2evolution/commit/43d8294932402d8236a5b4cadcffda90969304bb

(will be included in 6.7.4)

I added some images to a new page, saved the page as private [because the preview of a draft does not work in 6.7.3 ;-( ] and previewed. This led to the mentioned notice.

BTW: While previewing the draft I can see the changes I have made immediately, I first have to empty the chache to see the actual Changes when previewing it saved under privat e.g. So I hope, that this bug will be fixed.

Can you please confirm this is fixed in 6.7.4?

@fplanque thanks. the problem with preview a draft is solved in 6.7.4 - That works fine now.