How can I use the compose key for special characters?

On my Linux system (with KDE Plasma 5.13.4) I have configured the compose key to type special characters, like ö, è, ß or €. This works in my browser (as you can see), in my terminal and in my text editors. But it does not work in LibreOffice (v5.1.6.2), although it did work in LibreOffice before with LinuxMint. How can I get it to work again?

How did you do it? In the KDE settings or compiling a keyboard layout with xkb?

I used the KDE settings.

The problem was solved when LO 6.0 came in. Although not for the € which still does not compose in LO.

This is still a problem in LO NO compose key sequences work at all in LO, though they do in other programs.