Repeated Restarts When Waking from Sleep

I have a MacBook Pro running OS 10.10.5. The computer has started occasionally going through multiple restart cycles when waking from sleep. When this happens, I never get the login screen. I have to hold down the power button to shut down the computer and then restart. About 6 weeks ago, the original internal hard disk failed and was replaced with a SSD drive. But the problem did not start until a few days ago. There have been no other changes to hardware or software. The computer is connected to an external monitor and is on external power all the time, except when I travel or deliberately drain the battery for maintenance. I checked various discussions but could find no accepted solution to this problem.