You need to be able to
1) see the error groups accumulating under a merged error group
2) unmerge error groups from a merged group (individual error groups not unmerge everything)
If you accidentally merge an error or someone not knowing what they are doing merges error groups you need the ability to unmerge things.
Suggested here as well: https://raygun.io/blog/2014/09/errors-merged-wont-believe-happened-next/