Parameters for cylinder function in P5 (webgl) should be cylinder(radius, height) (reference) but on glitch seems to be cylinder(xradius, yradius) and no way to specify height.
Glitch doesn’t have any impact on the way you specify parameters in any module. Are you sure you’re using the same version of the module to the one the documentation refers to?
Ah that was it! Thanks. Someone’s template I started from was using P5 v0.6.0 and it turns out cylinder is not implemented properly until v0.6.1.