Ed Harris pulls his pulse ox probe off at 1:15. When they show the monitor, you can still see the pleth indicating the probe is still attached.
You can't pull out a urinary catheter like you see in the movie. You have to deflate a small internal balloon that holds it in place.
From approximately four minutes into the film and for about the next 30 seconds there are multiple shots of a shirtless musician in a dressing room. The film has been flipped, possibly to maintain the proper "eye line" in editing, making the tattoos on his chest reversed.
When Zoe examines Matt's old record collection, you can see several dozen LPs piled in a stack (in their sleeves, fortunately). No fan/collector would ever have kept his/her vinyls piled on one another horizontally, especially someone who eventually goes into the music business, it damages the grooves. You keep them upright (or vertical as it's called).
The drum kit Ben plays is too new to have belonged to Matt like Ben says. Those two haven't even seen each other for at least ten years, but the Sonor Vintage Series drum kit came on the market in 2015.
The scene shot outside the Chicago hotel is actually the Novotel on The Esplanade in Toronto. You can see the sign for the popular restaurant The Olde Spaghetti Factory in the background.