Some of you may notice that the imported subsite/subsites do not show up when you expand the “My Sites” dropdown menu. That is because your current user (that you are logging in with) is not associated with the subsite/subsites that were exported into the Multisite Network.
Let’s say you have just imported a subsite called cloud.migration.test.
In order for cloud.migration.test to show up in the “My Sites” dropdown menu, you will have to add yourself to the subsite “cloud.migration.test”.
To do that, go to Network Admin > Sites > Click Edit on a specific subsite (cloud.migration.test) > Users tab > Click Add User
Once you add yourself in there, you will be able to see that subsite (cloud.migration.test) in the “My Sites” dropdown menu.
You can check out further details about the “My Sites” menu on https://codex.wordpress.org/Dashboard_My_Sites_SubPanel