I think it often depends a lot on who the stakeholders are and what their priorities are. If the particular feature is urgent then of course what you describe is common. But when the priority is to maximize the number of features you're delivering, I've found that the client often prefers to do the bounded investigation and then work on another feature that is better understood within the same sprint, then revisit the investigation results at the next meeting.

But yes -- nothing prevents you from making mid-sprint reevaluations.

I'm not saying it never happens, but the whole reason for the planning poker process is to surface the things that might turn a 3 point story into a 13 point story, with everyone around the table trying to imagine what could go wrong.

You should not be getting 2-12 variance, unless it's a brand-new team working on a brand new project that is learning how to do everything for the first time. I can't count how many sprint meetings I've been in. That level of variance is not normal for the sizes of stories that fit into sprints.