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You could also use

SELECT GroupID,
       SomeValue
FROM   tablename
ORDER  BY AVG(CAST(0+CRYPT_GEN_RANDOM(4) AS FLOAT)) OVER (PARTITION BY GroupID),
          GroupID, --Just in case 2 groups get the same random number
          SomeValue; 

Or

WITH T
     AS (SELECT GroupID,
                SomeValue,
                CASE
                  WHEN ROW_NUMBER() OVER (PARTITION BY GroupID ORDER BY GroupID) = 1
                    THEN CRYPT_GEN_RANDOM(4)
                END AS rand
         FROM   tablename)
SELECT GroupID,
       SomeValue
FROM   T
ORDER  BY MAX(rand) OVER (PARTITION BY GroupID),
          GroupID,
          SomeValue; 

You could also use (Thanks to ypercubeᵀᴹ for the fix)

SELECT GroupID,
       SomeValue
FROM   tablename
ORDER  BY FIRST_VALUE(CRYPT_GEN_RANDOM(4)) OVER (PARTITION BY GroupID ORDER BY GroupID),
          GroupID, --Just in case 2 groups get the same random number
          SomeValue;

Online demo

You could also use

SELECT GroupID,
       SomeValue
FROM   tablename
ORDER  BY MAX(CRYPT_GEN_RANDOM(4)) OVER (PARTITION BY GroupID),
          GroupID, --Just in case 2 groups get the same random number
          SomeValue; 

Online demo

You could also use

SELECT GroupID,
       SomeValue
FROM   tablename
ORDER  BY AVG(CAST(0+CRYPT_GEN_RANDOM(4) AS FLOAT)) OVER (PARTITION BY GroupID),
          GroupID, --Just in case 2 groups get the same random number
          SomeValue; 

Or

WITH T
     AS (SELECT GroupID,
                SomeValue,
                CASE
                  WHEN ROW_NUMBER() OVER (PARTITION BY GroupID ORDER BY GroupID) = 1
                    THEN CRYPT_GEN_RANDOM(4)
                END AS rand
         FROM   tablename)
SELECT GroupID,
       SomeValue
FROM   T
ORDER  BY MAX(rand) OVER (PARTITION BY GroupID),
          GroupID,
          SomeValue; 

You could also use

SELECT GroupID,
       SomeValue
FROM   tablename
ORDER  BY MAX(CRYPT_GEN_RANDOM(4)) OVER (PARTITION BY GroupID),
          SomeValue; 

Online demo

You could also use

SELECT GroupID,
       SomeValue
FROM   tablename
ORDER  BY MAX(CRYPT_GEN_RANDOM(4)) OVER (PARTITION BY GroupID),
          GroupID, --Just in case 2 groups get the same random number
          SomeValue; 

Online demo