Only 80% of the Tsukuba Express trains are currently running due to the shortage in power that Japan is facing. From April 4, this will change slightly.
During certain hours on the weekdays (first train to 10am, 5pm to last train), the train schedule will be “almost” back to normal. From 10am to 5pm, there will only be 80% of the trains running. The weekend and holiday schedule will continue to have a limited number of trains.
Source: http://www.mir.co.jp/ (Tsukuba Express website)