Quite unusual timing and not easy to explain. Such dismissals usually happen in April/May or the fall. Brechalov was not a particularly unsuccessful governor, but those criteria have been eroded over the past years. His replacement is a local official, which Putin emphasized. Perhaps that's a clue.
The Moscow TimesThe president appointed Udmurtia native and former agricultural official Olga Abramova as acting governor until regional elections can be held.