If you have multiple Yammer accounts at different companies, you have several options to make sure you go to the network you intend to be on:
Close and reopen any open browser windows before you switch Yammer networks. If you have multiple browser tabs or windows open, some may maintain your identity even after you log out in one tab.
If you need to be signed-in to multiple Yammer networks at once, use a different browser or an in-private or incognito browser window for each Yammer network.
If you log in to Yammer, and experience one of the following problems, you need to contact your Yammer network admin:
You go to a different Yammer network than the one you signed into.
You are redirected to an account that is in your name but isn't associated with your messages or groups, and another account for your user name is displayed as Former member.
These problems result from configuration issues that only a Yammer network admin can solve. Network admins can find information to solve these problems in About Yammer networks and Office 365 tenants.