When you run a command in bash it will remember the location of that executable so it doesn't have to search the PATH again each time. So if you run the executable, then change the location, bash will still try to use the old location. You should be able to confirm this with hash -t pip3 which will show the old location.

If you run hash -d pip3 it will tell bash to forget the old location and should find the new one next time you try. //

for most bash features it's easier to use help instead of man, so here help hash