https://direct.mit.edu/qss/article/5/4/936/124788/The-disruption-index-is-biased-by-citation
Authors. Petersen, A. M., Arroyave, F. & Pammolli, F
Venue. Quantitative Science Studies 5 — full text
How the Institute flags it
frontier 5 times established 2 times
This source carries more than one flag across the corpus. That is not an inconsistency to resolve: the same work can be established evidence for one claim and frontier evidence for another, and the flag belongs to the use rather than to the source.