It appears that Russia conducted a third ejection test of the Sarmat missile, presumably at the Plesetsk test range on May 26, 2018 or a day or so earlier. There is no official confirmation and there is only one report at one of the NK forums, but the report appears to be reliable. I'll keep the question mark in the post title, though.

The first two ejection tests were conducted in December 2017 and in March 2018.

Sarmat20180511.png

UPDATE: Colleagues from Monterey took a closer look at the satellite imagery of the site. There was indeed some activity at the site a couple of weeks before the test. One can see it better on the planet.com site - that shadow may be the missile being loaded into the silo or being prepared for that. The Monterey folks were careful not to say anything definitively - the resolution is too poor for that - but these images certainly support the earlier information about the test.