This just seems to be how studio shows the value. Using the script below it will output the values.
local part = script.Parent
local cf = part.CFrame
while true do
for i=1, 100 do
print(part.Velocity)
wait()
end
part.Velocity = Vector3.new()
part.CFrame = cf
end
Studio does update the values but you need to reselect them, most of the time it does show this calue though.