It adds 3 and subtracts 1 instead of adding just 1

If you can please write one of the message of error you've.

"Indeed there where a lot of warnings on Timing Analysis due to pulse width violations."

I've not understood where you've this error (if it's in the compilation or when you run the simulator).

If I remember well that's a problem in the simulation that mean that you've designed bad waveform.

If that's the case in your simulation you should only move Reset and CLK, all other shall be "U" (that mean undefined - so not set).

To design the clock you shall use the "clock" button on the simulation weaveform vector file.

Moreover in your simulation are you trying to move the reset in strange way?

Or you move it only at the beginning (machine that start in reset and then it'll never been in reset).

If your purpouse is to move the reset with the button while you run the machine, it's better that you use a synchronous reset and not an asyncronous one.

So you put 2 register (2 because of metastability) after your input pin that will be clocked by your clock and modify your code as:

pr1: process(clk)

begin

if(rising_edge(clk)) then

if reset='1' then

nombre<="0101010101";

else

nombre<=nombre+1;

end if;

else

nombre<=nombre;

end if;

end if;

end process pr1;