When changing animation speed from KCM, the auto-hide panel animation breaks (showing and hiding panel becomes instantaneous and there is no way to bring it back). For works fine for windows. The animation works again affect reboot.
Sorry forgot to say, I'm on wayland, and here are the system info: Operating System: KDE neon 5.21 KDE Plasma Version: 5.21.3 KDE Frameworks Version: 5.80.0 Qt Version: 5.15.2 Kernel Version: 5.10.17-051017-generic OS Type: 64-bit Graphics Platform: Wayland Processors: 8 × Intel® Core™ i5-8350U CPU @ 1.70GHz Memory: 15.4 GiB of RAM Graphics Processor: Mesa Intel® UHD Graphics 620
Can reproduce. The hide/unhide animation becomes instant after changing the animation speed, but once plasmashell is restarted, the panel respects the speed again. I guess it's not receiving or interpreting the "animation speed changed" signal properly.
This seems to work correctly now, please reopen if there's still an issue in 5.24