I never used KDE2, KDE3.x was rock solid though. It wasn't until KDE4 where things took a massive nosedive and everything was crashing if you looked at it wrong - something that lasted until most of KDE5's lifetime, though by late KDE5 and now KDE6 it seems to be fine.
Well, "fine", for some reason Wayland sessions crash and restart the entire session whenever i press any key (doesn't happen with Xorg sessions), so i guess there are still some minor bugs to be fixed :-P
I can spontaneously remember k3b (CD burning tool) constantly failing because the CLI tools behind it (cdrecord, mkisofs, ...) replied in some way that k3b hasn't expected (e.g. because the locale was non-english, or the CLI tool devs changed the strings slightly, or there was a pointless warning text that k3b did not expect, ..., ...).
Admittedly, k3b was later... KDE3 era? But this is exactly how KDE1 felt... And in very bad days it still does today... You click on something, the developers assumed that the file manager can deal with it, but instead you just see the file manager saying "Unknown protocol" or similar. All the problems that arise when your system is very modular, but every module is a separate hobby project with no coordination.
I definitely loved KDE3 and was sooo excited about KDE4. And it was a pretty terrible disappointment. Nowadays I'm again fine with Plasma. Since mid KDE5 days.
> for some reason Wayland sessions crash
That's definitely a mess, too. I'm not fundamentally against Wayland. I'm using it right now. Even if it is still slightly broken today (yes, Wayland is a protocol; here I mean: the biggest implementations). But the entire Wayland story is very very sad. It took ages before it was at least usable for five minutes. And then everywhere the X11 support already gets disabled, while Wayland is still in a somewhat immature state. Sure, I somewhat understand what the devs say, and I can't force them anyways. But it's really not a success story for the Linux desktop.