Default Can't overwrite system

I am on VZ, have Malladus inttalled and 12B baseband
For the past month I have been unable to restore backups on any version of TWRP, even on freshly made backups. AT the end of the laborious system restore, I get a failed message.
So today I tried to dirty flash Malladus 1.29 over 1.24. After the ROM rebooted I went to the software info and it said 1.24. So I am wondering if the system partition or whatever is locked or corrupted. ROM otherwise runs fine.