It’s been noted across a number of Webmaster forums (in Russia) that Yandex may be having some issues in indexing new page content.
The first reported comment comes from around February 15th, with further comments and instances of it being mentioned throughout the past few weeks.
There are really problems with indexing in the last couple of weeks. New pages enter the index for a very long time (2-3 days), previously they entered within five minutes after the publication of the material.
Some troubles started with indexing. It has not been driving new pages into the index for a week. Prior to that, new articles were added to the index within five minutes after publication.
A week ago, I added sitemaps to all sites, nothing has changed, indexing has not become faster…
At the time of writing, there has been no official word from Yandex that an issue in the indexing process has occurred.