In the beginning of the final gun battle, French's weapon of choice changes from a Sten Mk II SMG (when looking over French's shoulder) to an MP40 (when looking at French head-on).
The M406 and M433 (two common HE rounds fired by the M203) arm somewhere between 14 and 27 meters (call it 45 to 89 feet). Felix's grenades should not have gone off in the final firefight.
In prior movie, Tommy had a Military Shadow box in his office with Air Force enlisted ranks. Headstone in this movie states "United States Navy".
During all movie French's Hyundai Accent is changing hatchback and sedan back and forth. For example, in escape from boxing gym scene, around 49 minute. Sue open rear door of hatchback and in the next shot sedan is visible, with different tail lights, etc. Hatchback license plate is "3THO479" and sedan is "8MCM110". Also, hatchback is fourth generation (2010-), and sedan is fifth (2017-).