Malicious attack or simply some error? Phone Self reset and keyboard is gone.

When I woke up today to get ready for work, my rooted Z740g was on the beginning tutorial for setting up the phone. While I was asleep the phone reset itself and erased everything I had on the phone storage. When I tried setting up the phone to see what was going on, the default keyboard app was not there! I had to use google voice to download a keyboard app from a website other than the google play store. No one had physical access to my phone and I had no other device sign ins on my google account history. I didn't grant any strange programs super user permission except for android lost. I didn't see any logs in androidlost and it uses my google account to sign in and I wasn't seeing any strange devices on that log. Do you think that this is some strange fluke or some type of malicious attack? My internal storage was almost full and occasionally my phone would reboot on its own and had various small bugs like battery monitoring being inaccurate on occasion. I'm worried about security breaches on my phone because I have seen how easy it is for someone to access the microphone, camera and any files on the device. I removed my sim and had to change all my online passwords.

Would flashing a rom completely remove any malware that might be on the device?

edit: I just noticed that there were two versions of chrome on my phone when I was trying to figure out what happened earlier today. I did notice that chrome looked different. I see a version 39 from before the wipe occurred and now I have version 28.0.1500.94 I looked up release dates and version 28 was released in 2013 and the phone wasn't even released until sometime in 2014. What gives?