Hi
[Square brackets are context info]
[There was an extraordinary event, and we would like to verify a hypothesis or figure out if something else happened. I would normally request support ticket, but corporate policy digitally restricts the use of any browser except Edge, and Edge has captcha load script error on support page, preventing to submit any ticket from my side.]
[TLDR: read only bold]
Observation: While having daily scrum, 10 of us witnessed Issues disappearing from our active sprint in real time, and finally the sprint has also become unavailable. Concurrently, another project's PO explained to me [Scrum Master] that she had an empty sprint from our project appearing in her project, so she decided to delete it as it made no sense to have our sprint in her project. Yes, the two events sound relating. What we figured out, the "lost" Issues got has landed in an old, deleted "Grooming" Sprint of our project, but using Issue browser we could set them to be in a brand new created interim sprint.
Question: Where/How can we check past actions on Sprints? (8th October in this case)
[We want know what happened on system level, and see if the specific user had relevant deletion action on our sprint, and if that has triggered the observed events.]
On Issues a generic log is available for all(?) users. [Issue logs show that user to set different sprint to each, but no info on the sprint]
On system events an admin access level log is available, but the past 3 months logs do not contain any sprint interactions (creation, start/stop, deletion, etc.) however we have ~100 projects running.
What would be the proper place, I could find such information at?
Thank you for reading and sharing ideas 
Zoltan