Making a linear regulator oscillate
Have you ever simulated a simple oscillator?
If not, start with a Ring oscillator: https://en.wikipedia.org/wiki/Ring_oscillator
In order to start ANY oscillator in a simulator you have to apply a pulse in order to &quot;disturb&quot; the circuit and make it oscillate.
In the real world this pulse isn't needed as noise will get the oscillation going.
It is a very common mistake (all beginners make it) to forget the startup pulse when simulating an oscillator in a transient simulation. Without the pulse the simulator will get stuck in the DC solution. That's an unstable solution but the simulator doesn't know that!
Edit: a good point was made by sstobbe, of course your DC solution has to correct and all transistors need to be biased correctly so that the loop has enough loopgain to even oscillate.