Thanks for the solution!
There is also an open ticket regarding this issue: https://core.trac.ww.wp.xz.cn/ticket/36510
Had the same problem!
Here is another thread about it which contains a working solution: https://ww.wp.xz.cn/support/topic/sidebar-drops-underneath-page-content?replies=11
There is also an open ticket which can be found here: https://core.trac.ww.wp.xz.cn/ticket/36510
