Know I'm a bit late, but maybe answer will be of use to someone else anyway.
Been using a Nokia 2720 for a while now, which uses KaiOS.
Haven't really encountered any bugs
really, but there's a significant lag in just general usage, and some things are not up to the standard of older dumb phones (smart phones only started becoming common in my mid teens).
Even just moving down the contact list can sometimes take what feels like a full second before it responds to the input. Not sure if this is particular to the model or a general KaiOS thing.
The T9 input method is kinda trash too, in comparison to how they used to work. Word order doesnt change in according to how often they're used, it's just a static order, and there's often garbage that aren't even words to skip over in order to reach the intended word. And since it's static, you'll have to do that every single time. Used to be quite fast at regular old-school T9, but it's just not possible on the KaiOS one because of all the extraneous input needed.>>2081
I wouldn't interpret it as rude, would guess you haven't gotten any response simply because nobody knows. First time I ever heard of a hypersim.