@grapevine as you haven't answered my questions, cannot with high assurance answer your questions. However, what I suspect (likely so does @Giuseppe Larosa ) there can be a noticeable difference in operational impact between a non stack member failing vs. the stack master failing. The latter, i.e. a stack master failure, can be more impactful, as it's the operational brains of the stack.
One issue, on many stacks, if the stack master fails, by default, the stack uses a new MAC for stack operation. However, there's often a configuration option to retain the original stack MAC even when the stack master fails. This often mitigate the impact of a stack master failure.
BTW, if the stack is being used for L3 operation, there are are often (?) other configuration options to minimize the impact of a stack master failure for those too.
Again, though, as you didn't answer my questions, cannot say with much certainty the cause of the behavior you note, but I can say, from experience, loss of a stack master can be more operationally impactful, especially if you've not configured the options to mitigate its impact.
