When the grandfather is explaining to the son what he thinks happened to the
boy's father, the grandfather makes a comment to the effect that he doesn't understand it all because he's not 'a specialist in quantum mechanics'. This movie deals with time travel and relativity, not quantum mechanics. Relativity deals with the large scale and quantum mechanics deals with the small scale. The reconciliation of the two has been the holy grail of physics, 'Unified Field Theory'. To object that one doesn't understand time travel because one is not a quantum mechanic is nonsensical. No physics professor would make that mistake.
When Erol and Gabe are playing chess the board is set wrong (the far left square at each side should be dark). Plus the move Erol suggests that might checkmate his father in three makes no sense at all, as "pawn 5 to pawn 3" can be neither a capture nor a legal pawn move.
The goof item below may give away important plot points.
The movie ends with Gabe being convinced to change his plans by a son from a timeline that now never comes into being. Since that timeline never comes into being, there's no alternate Errol to come back and save his father.