Krithi, there are a few things going on here...
- NextPlot is not contributing to the problem here. What you're running into is UIAxes cannot be GCA, which is why you aren't getting the results you expect.
- The other issue is the File Exchange chart you're using doesn’t support an axes parent handle. Instead it has a ‘lineprops’ input, so if you pass in a ‘parent’ option there, it will only affect the lines, not the axes.
- If the FX chart did support an axes parent option, in R2017a, the PATCH command would issue an error because it isn't supported by UIAxes (at the moment).
PATCH support in UIAxes is right around the corner, but even with that support in place, you'll still run into an issue unless a parent input is also supported in the shadedErrorBar chart.
Hope this helps!