Why has this issue just been closed with no resolution?

As mentioned bulk update is completely impractical.

If an issue has been in 10 Sprints then that single issue must be updated to add those 10 Sprints to the Sprint field using a comma separated string, if another issue has been in 8 Sprints then the same process needs to take place for that issue - individually! I cannot manually update each of the 1400 issues individually to put the correct Sprint information back into each Sprint.

I am hitting this same issue again now where components have been moved from one project to another.

I have just found this same issue.

This happens regardless of whether you change the issue type or not.

I moved 1400 issues from one project to another using the same schemes and same issue types.

The Sprint History was deleted from the records.

Only the latest (Active) Sprint information was copied, all other Sprints have been completely removed from all records.

This is a Critical bug in my opinion.

The above suggested workaround is not practical, because Jira uses the Sprint History for Reports on velocity etc. which have now been completely lost.

The workaround is to look in the issue's History for changes to the Sprint field, I guess

Honestly, Atlassian, I completely agree to Christopher that loosing sprints during migrations is a critical bug. 

If you are not providing a fix, what would be the workaround then?

We are encountering this bug. Should be higher than a low priority and a minor severity.