Words such as Röhrich with the ö represented as two code points LATIN SMALL LETTER O U+006F followed by COMBINING DIAERESIS U+0308 are not displayed correctly in the annotation stack view.... the COMBINING DIAERESIS isn't displayed.

If you use a single character with the diaeresis included then that is displayed properly.
Looking at the screenshot there does seem to be different fonts in use so it could be a font issue, or it could be an issue with how the text is being drawn into the custom swing component that displays the stack view.