Technical knowledge
Stabilising an emulsion and thickening it are two different jobs.
A thicker continuous phase slows the droplets down. It does not stop them joining. Viscosity buys time, and where the interface is not protected, time is all it buys.
That is why a sauce can pass its viscosity check and still separate on the shelf, and why raising the thickener is the most common answer that does not work.
Read the technical note
