Slack dough troubleshooting

So I have had a few occasions (esp. lately) in making Tartine Basic Country bread in which I end up with pretty slack dough in the final shape and proof.  Crumb ends up a bit dense, dry, and tough, crust is tough, with a grainy texture and is a bit thick but not very crispy.

I take these as indicators of degradation due to too much enzyme activity, and I'm looking for some confirmation and guidance on steps to take and what to watch.  I have been playing with time and temperature as I get a schedule that works for me, so it is not a big surprise. I do have a DIY proofing box for control, and the main changes I have made are trying to follow the instructions more closely in terms of temps - and so have been adding warmer water in particular for all of the stages. I also have a very active starter, which I think I am discovering the limits of.

In any case, one question I have is whether my over night levain build needs to be slowed/shortened.  In the morning, it is what I would describe as fully developed - not quite fallen back in on itself, but approaching that stage, as it collapses dramatically when I put a spoon in it.

The next culprit is my bulk fermentation...and here my temp.’s are at or just below those recommended in the book, and my time is right in the range recommended. I also thought I have been catching the dough near its peak...quite airy but not close to the point of collapsing.  I have not been using a straight sided graduated container to track volume increases, in favor of looking at how the dough looks and feels at each turn on the half hour. BTW - I am no newbie (but clearly have tons to learn!) and have made some very good loaves with this recipe, but I guess my judgment of the development of this dough and my system of controls needs work.  I could use input here as well, as I end up with dough that lacks elasticity and the bake ends up producing the poor qualities described above.

Not the ugliest loaf, but it really isn't very good...