Justine stabs Dorian with a small knife, in the very next shot, Dorian's shirt has the bloodstain but the hole in the shirt has disappeared.
After Dr. Seward knocks out Renfield, he very clearly falls to the left. The scene cuts to Seward, then back to Renfield, who is now lying in a completely different spot, towards the right.
Cunard line boats (such as the RMS Umbria) coming from New York would not go directly to London, but to Liverpool. From there, it would be much faster to board a train than another boat.