I see the behavior in the GIF, thanks. If it goes away after reopening the project then it is definitely a bug. My guess is something about the curves doesn't get recalculated. To be able to fix it we'd need to know how to get the curves in that. Unfortunately that may be difficult to figure out.
Do you have an idea what actions you took that lead to this? It's probably not easy to think back about the actions you took once you notice the problem, and the relevant actions you may have taken a long time ago. It'd be ideal to have exact reproduction steps, for example starting from a blank animation, create the keys a particular way. It could require copy/pasting keys or something else to trigger it though.
We'll keep an eye out for it. If you have an additional insights, those might help.