I must have seen a different movie than those leaving high reviews

Rating: 5/10 (30 December 2019)

This should have been a great movie.
I'm not going to go through the plot, as it's covered here many times over. I'm going to highlight the glaring issues with the film instead.
It's drawn out to the point that you almost don't care who did it, which is fine, because it's obvious who did it less than an hour in.
Marta clearly says within 5 minutes of the dose the patient would be showing symptoms and sweating, but that doesn't happen. Harlan never shows any symptoms whatsoever, and we know Marta is there long enough for them to present. This gave away that she didn't OD him.
Later on the film a person actually is given a fatal dose of the morphine around 8am (the same one that kills you in 10 minutes), but is magically alive at 10am when Marta arrives. 10 minutes =/= 2 hours. This was just incredibly lazy.
If you think someone is a murderer why would you set a meeting with them in a dark abandoned building with no form of defense?
Marta leaves her bag there daily, as were told. Why wouldn't Harlan just wrote a suicide note claiming he intentionally overdosed on morphine? Removes all the need for the whole mess if a sloppy cover up.
Overall, this movie is fun to watch for a bit, but becomes tedious because it's so lazy and flawed.