Something we didn't do in the construction is to place an insulation under the cooking bricks. So they sit on top of a 4 inch concrete slab.
I checked the temperature of the bottom of the oven (right above the area where I store the wood) and it got as high as 120F!
Should I be worried? Besides the heat loss, but is it normal that so much heat is going through the concrete slab?
It's not great...
You're probably not going to fire it enough to decompose/collapse the slab, but it complicates your heat management.
If you're planning to do long sessions, or plan to bake bread, you should fix it.
Most oven instructions call for insulation between the structural slab and the dome/floor bricks. If you can remove the floor, it's possible to place insulation inside the dome walls, and re-lay the floor. Calcium silicate is one of the best materials for under-floor insulation (especially if you're building the dome on it).
If it will only be supporting the floor, you can use one of the fiber boards like Insblock 19
or possibly the Roxul rockwool board
That will get you much of the benefit, although heat will still bleed down from the edges where the dome contacts the slab.
Some members here have demolished and rebuild their under-insulated ovens.