When using comet3() to displays a comet plot of the data specified in z versus x- and y-values matching the indices of z(a comet is an animation of a marker (head) and a line (tail) tracing a growing line over the data points), a single-point 3-D scatter chart is being printed.

[xmat,ymat,zmat] = peaks(100); 
xvec = xmat(:);
yvec = ymat(:);
zvec = zmat(:);
comet3(xvec,yvec,zvec)

fig2plotly(gcf, 'offline', false);

Expected animation and generated (https://chart-studio.plotly.com/~xarico10/845/#/) plot:

Examples on using comet3() can be found on:
https://www.mathworks.com/help/matlab/ref/comet3.html#responsive_offcanvas