science

In general:

It is hypothesized that contact with a single microscopic seed crystal of the new polymorph can be enough to start a chain reaction causing the transformation of a much larger mass of material.[5] Widespread contamination with such microscopic seed crystals may lead to the impression that the original polymorph has "disappeared". In a few cases, such as progesterone and paroxetine hydrochloride, the disappearance gradually spread across the world, and it is suspected that it is because Earth's atmosphere has over time become permeated with tiny seed crystals. It is believed that seeds as small as a few million molecules (about 10−15 grams) are sufficient for converting one morph to another, making unwanted disappearance of morphs particularly difficult to prevent.[3] It is hypothesized that "unintentional seeding" may also be responsible for a related phenomenon, where a previously difficult-to-crystallize compound becomes easier to crystallize over time.[5]

https://en.wikipedia.org/wiki/Disappearing_polymorph

The actual thing I was thinking of and not my butchered spelling:

During development—ritonavir was introduced in 1996—only the crystal form now called form I was found; however, in 1998, a lower free energy,[54] more stable polymorph, form II, was discovered. This more stable crystal form was less soluble, which resulted in significantly lower bioavailability. The compromised oral bioavailability of the drug led to temporary removal of the oral capsule formulation from the market.[53] As a consequence of the fact that even a trace amount of form II can result in the conversion of the more bioavailable form I into form II, the presence of form II threatened the ruin of existing supplies of the oral capsule formulation of ritonavir; and indeed, form II was found in production lines, effectively halting ritonavir production.[52] Abbott withdrew the capsules from the market, and prescribing physicians were encouraged to switch to a Norvir suspension.[55] It has been estimated that Abbott lost more than US$250 million as a result, and the incident is often cited as a high-profile example of disappearing polymorphs.[56]

https://en.wikipedia.org/wiki/Ritonavir

But thanks for actually asking.

And sorry I guess for being off a decade, names and dates aren't as easy for me as concepts and science.

There was a recent Verstasium video about it.