Ken Goe has this
'There were signs of strain this year between Johnson and Maurica Powell. While the UO head coach was publicly supportive, one source says the relationship between the two had become difficult.
Johnson keeps a tight rein on his program. Assistants rarely speak publicly.'
Also says'
The men's program under Andy Powell had fallen off a little in recent years, although the Ducks still were producing top-notch individuals. Sam Prakel, for instance, was third in the mile indoors and sixth in the 1,500 meters outdoors at this year's NCAA Championships. Edward Cheserek was lights out for four years.
There is much less margin for error on the men's side. Men's track has 12.6 scholarships, which magnifies an injury or recruiting mistake.'
https://www.oregonlive.com/trackandfield/index.ssf/2018/06/how_will_the_ducks_go_forward.html
Register Guard has nice quote from Robert Johnson
' We are very excited for Maurica and Andy and this tremendous opportunity," Johnson said. "They have been a huge part of this program's success over the past 13 years, and we are extremely grateful for all they have done for the Ducks. ..
http://www.registerguard.com/sports/20180618/coaches-andy-and-maurica-powell-leaving-oregon-track-and-field-program-for-washington