@antonioabb 

Router mode would be more hardware intensive (CPU, RAM) vs Access Point mode.   It could therefore be that the device is working a bit harder in Router mode and this slows the WiFi rate.

However... my honest opinion is its just a red herring / rounding issue.    WiFi is so erratic at times this is likely just down to a channel change after mode switch, interference or something like that and not anything to be concerned about.

In a WiFi world, differences of +- 50mbps is nothing to be concerned with and will happen regularly.

  @Philbert mmm I did many tests changing channel width, and more. but the result does not change .... for me knowing that I have 320 megs but 270 arrives bothers me, so I leave it in access point mode