We usually have a 2-week sprint (10 working days) and during this time we hold 2 sessions of 1 hour each for backlog grooming. In backlog grooming, we discuss the stories in product backlog and if fairly simple, the dev team estimate it as well there n then.
The dev team hesitates to estimate it without knowing the exact solution to the problem. In that case, they then reach out to their manager (based out of US) offline and come back with the approach either in the next grooming session of estimate it offline. By the 2nd backlog grooming session, we somewhat know in our heads how our sprint backlog for the next sprint would look like (exceptional scenarios not included when there is a last minute story addition, prioritized by the business).
My issue is, what if we have a story that requires thorough technical discussion, and requires the manager who is in the US, presence as well. Do we need to entertain the story in backlog grooming or can we keep a separate session (besides backlog grooming and sprint planning) for this vast technical story?
I am thinking to get all the stories discussed in backlog grooming and get this heavy one discussed out of that in a separate session. Once discussed, it can be then estimated. Once estimated and pulled in sprint backlog, we can then discuss the approach to technically achieve it in sprint planning session.
First, to answer your immediate question ...
Do we need to entertain the story in backlog grooming or can we keep a separate session (besides backlog grooming and sprint planning) for this vast technical story?
... the Scrum Guide states, "The Scrum Team decides how and when refinement is done." I.e., there is relatively little detailed guidance or prescription from the Guide in terms of how to refine. Try a few different approaches across different sprints and continue to inspect & adapt.
It may help for the team to explore approaches to breaking up those backlog items that require thorough discussion. (For example, figuring out if the backlog item can be further "sliced vertically" may be one approach to try.)
The lingering question that is implicit from your post is why the development team has a manager who is not part of the team but whose technical input is so critical. If this is an outside expert who is only occasionally consulted, this may not be a major issue. But if the Development Team is heavily dependent on the input of someone who is not a member of the team, then this dependency will likely add unwanted complexity and may result in other unforeseen consequences, as well as having the potential inhibit the team's own growth.
See, in particular, this description of the Development Team from the Guide:
Development Teams are cross-functional, with all the skills as a team necessary to create a product Increment
If this is not reasonably true, then there may be deeper issues to address in parallel with improving the refinement process.
Thanks Andrew for reverting.
It is not that the dev team is highly dependent on their manager who is in the US but on few occasions, they do need him. As of now, the PO has created only one story for this issue since we wanted to have a thorough discussion on what they want before telling the PO how to split them up.
I will have a separate session as of now and would see how it helps and would adapt to a different approach if required.
Think of refinement (or grooming) as an ongoing activity rather than a session. A team might allow up to 10% of the time during a Sprint to accommodate this. Refinement might consist of some sessions, or ad-hoc workshops, of even spike investigations.
The purpose of the activity is to know enough about the work for it to be estimated and “ready”, so that Sprint Planning is de-risked and can be conducted without impediment.
The situation may change if and when multiple teams are involved. Backlog refinement may then need to be managed as an actual event.