CTBTO monitoring stations positioned along the Nyonoksa accident's modeled plume path stopped transmitting data, and a senior Russian official's own remarks suggest this was not a technical malfunction

CTBTO atmospheric transport modeling projected that the Nyonoksa accident's radioactive plume would pass over specific Russian International Monitoring System (IMS) radionuclide stations — Dubna, Kirov, Zalesovo, and later possibly Norilsk and Bilibino — between August 10–13, 2019. Per Spykman et al. 2021, "radionuclide data from these stations were never received by the CTBTO's International Data Centre in Vienna." CTBTO Executive Secretary Lassina Zerbo tweeted on August 18, 2019 that the organization was working to resolve "technical problems" at Dubna and Kirov after they stopped transmitting; Zalesovo, Peleduy, and Bilibino subsequently went dark too. Two days later, Russian Deputy Foreign Minister Sergei Ryabkov stated that data transmission to the CTBTO "was voluntary, and in any case was not subject to the organization's consideration" — which Spykman et al. read as "indirectly admitting that the cessation of data transmission was not due to technical problems." The Hecla–Kemp paper independently states the same fact in its own background section: "Russian CTBTO-IMS detectors were strategically deactivated along the anticipated plume path over the following week."

This is a coverage gap, not a negative detection result — distinct from the Spykman et al. null result, which came from filters outside the plume path rather than from the silenced stations inside it. The monitoring infrastructure built to answer exactly this question did not produce data.