Move ROI points within app designer

I have x, y values for a line, I'd like to display this line as an ROI line like one created by drawpolyline and then I want to be able to edit the points along the line using my mouse to drag them around. I created a similar app that worked fine using GUIDE but updating to app designer seems to make it imposible to move the points. Here is a simplified version of what I'm doing:

In the startup function:

app.p0 = drawpolyline(app.MainImageAxes,'Position',[0 0],'Visible','off','InteractionsAllowed','all');

In the "Edit line" button callback function:

app.p0.Position = [x y];

app.p0.Visible = 'on';

This successfully creates and draws the line using my x, y values and it looks like an ROI I should be able to edit but trying to drag the points around does nothing. I tried adding draw(app.p0) at the end which just cleared the Position data and made me start creating the line from scratch. When I double click to finish the line I am still unable to edit the points however.

Thanks in advance.