To me, it appears the previous timeseries YAxis Limits have not changed (i.e. it is still "zoomed in"). I think what has happened is that, by adding a plot requiring an exponent to capture the scale of the Y values (x10^6), the actual height of each plot has also shrunk to to accomodate an exponent. The fix is to find a way to plot the data without adding the exponent for the larger scale variables.
One approach may be to divide by whatever the explonent is.
nexttile
y1 = randn(1,2841)*1e6;
% find exponent automatically and divide y1 by it when plotting
x10=floor(log10(max(y1)))
plot(x,y1/10^x10,'LineWidth',2,'Color','b')
I wonder if stackedplot might be a better option for you. You'd have to modify your code a little, and wouldn't be able to color each line (at least not easily), but it does a better job keeping the y-axes as tall as possible.
figure;
chans = 16;
for subplotN=1:chans-3 %plot first set of time-series
x = 1:2841;
y(:,subplotN) = randn(2841,1)*50;
end
y(:,subplotN+1) = randn(1,2841)*1e6;
stackedplot(x,y)
