Question

Why the is .. else construct does not work in CMD? It is in loop with EnableDelayedExpansion

IF ( !Delay! LSS !low_delay! ) ( SET priority=1 ) ELSE (
    IF ( !Delay! LSS !average_delay!) ( SET priority=2 ) ELSE (
      IF ( !Delay! LSS !high_delay! ) ( SET priority=3 ) ELSE (  SET priority=4 )  
))

Answer 1

Your syntax is simply wrong.
Brackets are not allowed in the condition.
The brackets must be on the same line where the ELSE statement is.

IF !Delay! LSS !low_delay! ( 
  SET priority=1 
) ELSE (
    IF !Delay! LSS !average_delay! ( 
        SET priority=2 
    ) ELSE (
        IF !Delay! LSS !high_delay!  ( 
            SET priority=3 
        ) ELSE (  
            SET priority=4
        )
    )
)