Stretch Infinite autostart loop from .profile, fail from rc.local

[Doug Coulter]

A general issue with autostarting things via various methods.
Testing with xtightvncserver and conky - starting in .profile results in a new instance every second till 100% memory and cpu are used and system basically becomes unresponsive.
Tried both with and without trailing &.

"touch" works in /etc/rc.local.

This in rc.local:

touch /home/pi/pretest
vncserver
touch /home/pi/posttest

produces only a pretest file in /home/pi.
adding an ampersand to the end of the vncserver line results in both files created, but no vncserver running.

vncserver works from a prompt, FWIW.
I am waiting for network on boot in all cases.
This all works to perfection in Jessie on many pi systems here.

Pi 3 b+ won't run Jessie....This renders the Pi 3 b+ useless.

Trying a desktop file in /etc/xdg/autostart like this:
[Desktop Entry]
Type=Application
Name=xtightvnc
Comment=vnc server
Exec=vncserver &

does not work. Removing the ampersand results in vncserver being started an infinite number of times (like all other methods tried that start it at all). You have to move fast to edit any of this before the pi locks up, or just pull the SD card and edit in another machine.

Sorcerer's apprentice bug. Someone made a real nasty mistake here.

I can't use realvnc because it won't work with the viewers on all my other systems - tightvnc does. And this is just a surrogate test, I am having this issue with ALL things that I want to autostart, all of which work fine on Jessie (and also on PCs running mint/mate).

bug #1756553 reports a 1/second issue with something else - this is also a 1/second issue.
Something is basically borked that has this heartbeat.