According to Voenno-boltovoy kanal, one of the Russian Telegram channels devoted to military developments, Russia was planning to conduct a launch from the Plesetsk test site toward the Laptev Sea on 29 May 2021. These kind of notifications are normally issued before a test of the Nudol ASAT system. The most recent one, confirmed by US Space Command, took place in December 2020.
Note that the 29 May 2021 NOTAM is a bit different - unlike in December 2020, this time there is no keep-out area over Novaya Zemlya. But the test in April 2020 also did not close Novaya Zemlya, so maybe it was the December 2020 test that was different.
It is not known whether the test actually took place - Russia normally does not announce these tests and US Space Command did not comment (but it was noticed by Robert Wood, U.S. Ambassador to the Conference on Disarmament).
Comments
Does someone have an educated guess where we could assume the launch site?
There was rumors about LC32 but it turned out as something what seems to be a Sarmat fuelling station ( 62.905467° 40.788286°).
The Yars launch site LC 167 seems to be unlikely but feasible.
Another possibility would be the former R-16 site LC5 (62.984151° 40.775484°).
Any ideas?
Cheers