Downgraded to Kitkat phone worked at first then slowly begin crashing

I sent my phone into Samsung for a repair and they replaced the motherboard, the screen almost a whole new phone. When it was returned they had already downloaded lollipop which towelroot would not work. Found a site that showed me how to downgrade back to kitkat root, install safestrap and I could return to lollipop. I never did the lollipop part as I did not like it much. It worked great at first I was able to return back all my data. After a week it begin to act funny, not wanting to wake up from sleep and then slowly apps begin crashing and not working. I would restart my phone and things were fine. Another week apps were crashing left and right and then my data begin disappearing like my messages and the levels of my saved games. Then it begin restarting on its own 3 times during the night. I tried to reinstall the rom and re-partitioned the phone and did factory reset but it continues to periodically restart even though I have given up on reinstalling my data since it factory resets on its own. I guess I am in a very slow bootloop. Can anyone suggest what I can do? Thanks in advance