Plot hole: The motivation of the cult in this film - a dark entity trying to birth their demonic god - is completely different from the cult of the original film, which was portrayed as fanatical Christian witch-burners. No satisfactory explanation is given in the film to explain this and in fact the film explicitly implies they are the same cult on several occasions. The explanation that the cult of the original film is some sort of offshoot or different sect of the cult from this film cannot explain this as it is pure fan speculation and conjecture (thus non-canonical) and in fact raises several more plot-holes.
Plot hole: When the CIA detects that Matt is accessing sensitive information to track Frost, they trace Matt's location and find out that he is using a public computer in a cafe. We then see that Matt is viewing the same kind of software, files, etc. that the CIA views at their agency. There is simply no plausible way that a random public computer would have CIA software, or be able to access CIA data at all, regardless of Matt's clearance. The computer itself would have to be on a secure domain.
Plot hole: The killer has been living in the (apparently big enough) crawlspace between walls and floors, for over a decade. There is no explanation (or rationale) given on how he moved the various objects inside every room, closed doors, fed when the house was not occupied, hid the various corpses and, silly detail, concealed his own BO and the stench of his own living quarters, which is something hinted at when they find out his hideout. It is explicitly said that he is agoraphobic and does not get out, ever.