Serial.readBytes() reads characters from the serial port into a buffer. The function terminates if the determined length has been read, or it times out (see Serial.setTimeout()). Serial.readBytes() ...

In version 1.9.3 it used to work correctly. Now, version 1.10.0, it always returns 0, while available() returns a positive value. If relevant, in my case I have a timeout set to 0. I'll post here ...