Hi,
please check in settings that "Recent Tabs" feature is enabled in settings.
If still not working, close SSMS and find this folder:
C:\Users\YOURLOGINNAME\AppData\Local\Solutions Crew\Ssms2014\Recent
Rename it to, say, "Recent_BACKUP"
Start SSMS.
SSMSBoost will re-create the folder and will start writing session info.
If feature will start working, this means that some file was corrupt.