Hi Janilyn,
I have exactly the same issue as other users here. I can log in with my user, swap to another user successfully, but when I try to return to my user it logs me in as a completely different user and this is causing major issues for my client.
I have copied the website into a staging area and downgraded the plugin to version 1.2.7 and everythig works correctly. So the issue was introduced in version 1.2.8 and above.
Hope this helps.
And thank you for a great plugin.