I have two of these and both work. Both the original from years
back and the II. I use them as a quick check for the mobile and
the other for portable.
Simple answer is some part is in the wrong place (wrong value)
or your soldering is not as good as you may believe especially
on the the leads of the toroid transformer. The critical parts are
R1,R2, R11,R12 and the transformer T1. assembled wrong or
bad soldering will cause problems.
In normal use the LED will be dimmer at 28mhz but with a 50 ohm
load it should not eve be on at any frequency as 50ohms is a
good match. As the resistor value departs from 50 ohms the
led should light and get brighter depending on the value
difference from 50 ohms.