It caked, or the yeast died
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Caking is moisture
Fine powders take up water from the air and from the headspace and then bridge into lumps. Baking powder, cocoa and confectioners sugar are all prone to it, and a clear jar shows it clearly.
Which makes the liner the component to specify
Of the 244 closures on this shelf, 69 carry an HIS induction-seal liner, 41 F217, 31 pressure-sensitive and 27 none at all. A gasket seals while the cap is tight; a bonded membrane seals until somebody opens it.
Headspace is where the moisture sits
A part-filled jar holds air, and air holds water. Filling consistently and leaving no more headspace than needed is a real control, and it also makes the product look better.
Yeast is not an inert powder
It is a living organism whose activity declines with time, moisture and heat. The archetype treats all nine leaves the same way, and for this one the container is preserving viability rather than texture.
Baking powder has a shelf life for the same reason
It works by a reaction that moisture starts. A jar that breathes gets a product that has partly reacted in storage and underperforms in a cake, with nothing visible to show it.
Light matters for some colorants
Dyes and lakes can shift under light, and 18 amber and 19 black containers on this shelf exist for that. Against 51 clear, which sell the product, that is a trade to make deliberately.
Keep retained samples and open them later
From each packing run, stored as stock is stored, and checked at intervals. Caking, color shift and lost leavening power are all slow, and only a retained sample measures your package rather than your recipe.
Say what the storage advice is
Cool, dry, tightly closed, and for yeast refrigerated after opening if that is what you mean. Customers follow storage advice when it is specific, and the alternative is a product judged on how it performed in a warm cupboard.