Stuck Fermentation. I'm at a complete loss...

Why did you move your beer off the yeast after 6 days? I don't think that helped your cause. I would try pure O2 , a much longer primary and reyeasting next go round.

 

As was already mentioned the transfer after only 6 days was not helpful.

Do you conduct a transfer to a secondary for your other batches as well? If so, I would recommend that you nix this step. Unless you are doing something like adding fruit or oaking your beers there is no need to conduct transfers to a secondary.

Cheers!

 

Did you rehydrate your yeast?
Do you ever make lower gravity stouts?

 

Don't transfer to secondary unless aging with oak or fruit, etc.

And even then don't do it after six days. Let the yeast do its job, sometimes this takes quite a bit of time; especiAlly so with high Gravity brews.

Rehydrate your yeast prior to pitch. Try to keep temps of yeast slurry as close to the wort your pitching into.

Really your bigg at issue is moving your beer WAY too early. Let the yeast do its thing and be patient.

Also, storing at 68-70 degrees ambient temperature is too hot. Your likely getting a varried temp range of 70-80 degrees inside the fermenter during active fermentation. That's just too hot for US 05 and most other strains.

Lots of easy and cheap tricks to get temps down; just look them up.

You may want to try doing a stout in the 1.050-1.070 range also.

 

Your yeast are not happy because you are not giving them enough oxygen. Here are the details on when pure oxygen is required.

At 1.097 this is a huge beer . . . which sounds like an oxymoron for a one gallon batch. But those yeasties are gasping for something to breathe and shaking is not gonna get you there. In Yeast, it is recommended for OG's over 1.083 to add a second dose of oxygen after 12 - 18 hours of fermentation (after first cell division).

Fermenting US-05 at 68-70 air temp is on the warm side. While this should make the yeast more active, the higher temps reduces the oxygen level (see link) and can produce fusel alcohols. My suggestion is to start the wort in the mid 60s and don't let it rise to 70 until after day 4 or 5. As recommended by @jlordi12 , let it ride in the primary for at least two weeks+.

Getting setup for adding oxygen and precise temp control is a chore, but it pays off.

 

What they all said.
Things to try:
rehydrate yeast, or make a starter (through with 1 gallon batches that may not be needed.
use the full packet of yeast - and on that note, double check the age - make sure the yeast is fresh.
Leave in primary for much longer.

 

With a beer that big (1.097) I would leave it in the primary for a minimum of 2 weeks before I even bothered with a gravity reading, then I would probably leave it for another week or to so it definitely finished. Then I would not bother with a secondary at all.

 

A few observations / suggestions from a fellow <5G batch-size home brewer:

• Pitching 1/2 dry yeast packet (~ two level teaspoons) into a 1G batch-size is serious overkill.
  One level teaspoon is more than enough.
• Instead of shaking to aerate the wort ... use a (stainless steel) whisk.
  Once after racking from kettle to the fermentor for a minute or so then again after pitching the yeast.
• Ferment at a lower ambient temperature (low-to-mid 60s).
• Taking a gravity reading from a 1G batch-size is impractical.
• Ferment in the primary three full weeks (a little longer is better than bottling too soon).