I was using Nvidia graphics card and the Nouveau display driver, this seemed to cause the problem.
I moved to a proprietary Nvidia driver, rebooted and suspend now works fine.
So I would suggest checking what driver you are using and changing to the proprietary driver available for your system.
Check in: SYSTEM SETTINGS / SOFTWARE & UPDATES / ADDITIONAL DRIVERS
I was using Nvidia graphics card and the Nouveau display driver, this seemed to cause the problem.
I moved to a proprietary Nvidia driver, rebooted and suspend now works fine.
So I would suggest checking what driver you are using and changing to the proprietary driver available for your system.
Check in: SYSTEM SETTINGS / SOFTWARE & UPDATES / ADDITIONAL DRIVERS