loop compensation uc3845
OK, I read the appnote and I see what you are trying to accomplish.
Since you started on this road, you may need to continue, since reducing the frequency may mean redesigning the transformer.
I am not at all crazy about the way they change the operating frequency. You can take a look at this appnote:
https://focus.ti.com/lit/an/slua165/slua165.pdf
The frequency foldback is used here for overload protection situations, but you can apply it to your case, by simply changing the transistor to an npn and feeding it with a voltage derived from the input voltage. That way your frequency changes in response to the input voltage. It does not really need to do a continuous frequency sweep, if it switches at some point (say 240VAC), that should also be fine.
Variable frequency is not a bad idea for such a wide input range. The thing is that with a variable frequency it is harder to tell when your circuit is oscillating and when not. So until you fix all that, you may consider making the changes I suggested in the previous post and set the frequency to the lower value and simply test at high line only, until you get it to work. Then you can raise the frequency and test at low line.
When you are done, you can again try the approach of the appnote.
By the way, Ve means the error amplifier output voltage (pin 1).
I would check to make sure the auxiliary winding is connected properly (not reversed). The fact that the auxiliary voltage changes so much with the input voltage kind of makes me think it might be reversed.