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James River Group  (JRVR - Get Report) shares on Wednesday lost as much as a quarter of their value after the insurer said it canceled all policies issued to its biggest customer, Uber  (UBER)  subsidiary Rasier.

On the news B. Riley analyst Randy Binner downgraded James River's stock to sell from neutral and cut his price target to $40 from $45.

The stock of the Pembroke, Bermuda, company at last check was down 22% to $38.01. It had fallen as much as 25% to $36.42.

James River said it delivered a notice of early cancellation, effective Dec. 31, of the policies, which are included its commercial auto line of business. A majority of the insurance policies were due to expire on Feb. 29, 2020, it said.

"This account has not met our expectations for profitability, and we think it best to terminate the underwriting relationship as of year end," J. Adam Abram, chairman and CEO of James River, said in a statement.

An Uber spokesperson told the Wall Street Journal that James River was one of four insurers the company worked with in the U.S., including Farmers Insurance Group, Progressive Corp. (PGR - Get Report) and Allstate Corp. (ALL - Get Report)

"James River insures the ride hailer's drivers in 20 states, D.C. and Puerto Rico," the spokesperson said. 

The Journal report also said Uber expected to bring in another insurer to replace James River, but it didn't provide details.

Uber shares were down 0.9% to $29.03 on Wednesday.

James River also said two key items would affect its third-quarter results. One is an "adverse development," valued at $55 million to $60 million before taxes, net of reinsurance recoveries and reinstatement premiums. 

It's related mainly to its commercial auto line of business within its excess and surplus lines segment, for the 2016 and 2017 underwriting years. The rest of these losses, less than $10 million, relate to prior underwriting years in casualty reinsurance, the company said.

It also said gross written premiums in its core non-commercial auto excess and surplus lines grew 72% from the year-earlier quarter.

In a note, Binner said the Rasier account represents about 20% of the insurer's trailing 12-month premiums and about 35% of trailing 12-month premiums in the E&S segment.

He also said James River disclosed a roughly $2-a-share reserve charge related to the Uber risk, which is about 3% of total reserves.

"While [this] is manageable based on these figures, concern around reserve adequacy is likely to remain an overhang on shares given the termination of the Uber relationship, a significant move," Binner wrote.