MacPro 5.1 freezing after login

Dear All. I hope everyone is doing well. I have a MacPro 5.1 with Mojave running. It as been running without issue for more than a year until recently, the two last time I started the Mac it is freezing after login. It is login as normal but as soon as I touch the mouse, the curser will disappear and the Mac will stop to respond. No Mouse, no keyboard and the Mac is frozen because I can see the istat indicator stopped moving. The only thing I can do is press the power button for several second to shut it down. On the next start up it will work normally. Again this is a new issue, never had that before so I don't think it's Mojave. It started to behave this way after a failed attempt of transferring files from external hard drive to an other using Carbon Copy Cloner. The source external HD is getting old and stalled during the process creating an error. I had to force to quit Carbon Copy Cloner and disconnect the external HD. It is after that, next morning at start up, this issue has started. Therefore I am assuming that after this failed transfer attempt it might have created a bug. This is all I can think of. I have not done anything yet. I will probably do the usual. reset the NVRAM or reinstall Mojave. However, any suggestions would be welcome.

Thank you in advance for your time.