System is broken maybe because you used an old TWRP (version inferior than 3.5) to install the latest ROM...
Yes, the latest Official TWRP for your device is a little broken for installing ROMs but you can use another TWRP based on the version 3.5 like
twrp-3.5.A9-grus-geoanto555.img -or- twrp-3.5.2_9-1-grus-KudProject.img
Try to install the latest ROM with one of these custom recoveries and if it doesn't work, do a clean install (= "Format Data" button in "Wipe" menu of TWRP) then it should be good.
EDIT: Anyway it's recommended to do a clean install when switching branch (Beta <-> Stable).