@marzzbar - Can you give us a bit more on the replacement SSD you used. Did you buy another custom Apple unit or use an adapter to then install a M.2 SSD?
As to why the display image gets a bit mangled can be because of the CPU or RAM is having issues. I would restart the system and run the onboard diagnostics to see what it tells us by pressing the ***D*** key.
Reference: [https://support.apple.com/en-us/102603|Mac startup key combinations]
Let us know what the error messages are.