I've downloaded a fresh Raspbian image and built a system on my lovely new RasPi 3A+.
When I try to connect with VNC from my MacBook Pro I get the message: 'The connection was refused by the computer' for about ten minutes, after which the connection is accepted and everything else seems OK.
Investigating further, I find that I can avoid the delay if I plug in my USB hub and either a mouse or a keyboard (all are USB 1).
The thing is, though, that if I put the same card into either a 3B+ or a ZeroW there is no connection issue - VNC connects as soon as the OS has finished booting.
I'm starting to suspect that the fault lies in the board rather than a configuration error but, for what it's worth, what I've done is :
Loaded 2018-11-13-stretch-full.img from raspberry.org.uk
Set up Wifi as part of the installation
Enabled SSH, VNC
Reset pi account password
Set new computer name
Copied wallpaper pictures to /pi/pictures and set one up
Updated/upgraded with apt-get
Edited /boot/config.txt - uncommented following lines and changed framebuffer_height to 700:
Installed FORTRAN and speedtest
sudo apt-get install gfortran
sudo apt-get install python-pip
sudo pip install speedtest-cli