SUMMARY It seems like that the shortcuts "Next terminal" and "Previous terminal" are in conflict with each other. If both of the two shortcuts are set, only one of them could work. The other one will trigger a "Ambiguous shortcut detected" dialog box. STEPS TO REPRODUCE 1. Settings -> Configure Shortcuts 2. Set arbitrary shortcuts for "Previous terminal" and "Next terminal" 3. Use the previously defined shortcuts for previous/next terminal OBSERVED RESULT -> The shortcut for "Previous terminal" will trigger "Ambiguous shortcut detected" dialog box, even if it is not ambiguous at all and there is no conflict. EXPECTED RESULT -> Previous/Next terminal shortcuts should work if they are not ambiguous. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Ubuntu 18.04 (available in About System) KDE Plasma Version: KDE Frameworks Version: 5.44.0 Qt Version: 5.9.5 ADDITIONAL INFORMATION
*** Bug 410038 has been marked as a duplicate of this bug. ***
Seeing the same issue
This started to work for me somehow. I've updated X.org to 1.20, switched to libinput, updated Plasma to 5.18.4, KF5 to 5.69 - and now shift+tab works for me in yakuake.
Since this seems to be resolved, I'm closing this bug.