Sorry to hear you're having problems. I've been using a Digiflash routinely for the last 11 months with excellent results. It tracks my Gossen Luna Pro F "perfectly" within the 1/3 stop limits of the Digiflash readout.
I do have one word of warning. The meter seems to take a reading over a very short time frame (called a "gate time" in electronics), likely shorter than the typical 50-60 Hz AC cycle, which leads to odd readings under flourescent or similar lights. See my article on APUG. To get an idea if it's doing this, hold the metering button down and watch the +/- relative exposure indicator. If it cycles quickly up to a stop or two, you might be in a situation where gate time is shorter than the cycling time for an electronically cycled AC light source.
Almost every Gossen digital meter I have owned (the exception being the spot meter) has eventually needed to have the button pad replaced or the button contacts cleaned. This with a professional workload of being used almost every day. I don't think that should be the case with a new meter, but the symptoms described in the original post are identical to what I have experienced when cleaning or pad replacement is needed.
Just to make the story complete (for now): My digisix was sent for repair under warranty 3 weeks ago; I was contacted that it would be replaced (with a new one) instead of repaired, and last week I received a new digisix.
This one hasn't shown a single problem (yet).
To come back to the original poster's problem: this is exactly what I saw with my "old" digisix: at the moments that it DID work, it always measured EV 9 (plus/minus 1).
And just for the record: I'm happy with the service delivered by Gossen.
-- A sinister little midget with a bucket and a mop / Where the blood goes down the drain --