Kate does not work well with keyboard navigation. https://mail.kde.org/pipermail/kde-accessibility/2018-November/003253.html
I can confirm that with Kate (unlike other applications the key press for up keys is seemingly not sent. The Qt stuff uses a relatively crude global event filter, presumably that's where to look. This is not technically related to Plasma, but I don't feel like staring a new board, but want to track this somewhere.
https://codereview.qt-project.org/#/c/245319/ presumably fixes the keys not being sent.
This is kinda blocked on getting the patch into Qt, that's a more general solution instead of hacking around it in Kate.
You can build Qt and run Kate with the patched Qt version. Sadly the change to Qt needs more work and I haven't gotten around to it for a long time :(
ah ok. if i read some of joanies messages, it feels that it will fix some more issues too.
This seems to be fixed. Orca reworked the way how shortcuts are grabbed and speech is interrupted on focus change. I assume this fixed it.