Usually when the yellowing begins at the oldest leaves first and works its way up progressively through the older leaves ... and the yellowing is uniform yellowing with no black spots or ringed blotches on the leaves ... that is a sure sign of the plant robbing nitrogen from the older leaves and transferring it to the new growth ... meaning your plants are asking for a nitrogen boost. However, I don't see the "yellowing" ... all I see in your pictures is some off-color, dull khaki colored leaves like in that third picture, then it seems the coloration goes to dry, dead, dark tan or light brown. Also, look at that first picture and the last picture where the discoloration seems to have skipped past some of the older leaves and is well progressed on a some of the foliage in mid-plant. That doesn't seem indicative of typical nitrogen deficiency which would seem to be the first deficiency that would appear if indeed you are flushing or leaching out nutrients by over-watering as N is more unstable and "leachable" than P or K ... and you say you're fertilizing regularly with Miracle Grow. So, I don't really suspect it's lack of application. I'm thinking possibly disease of some sort. I'm not familiar with Miracle Grow plant growing mixes, but I did have trouble this summer with a knock-off brand of the same type stuff from Scotts (which I think is the same company now) where it was just to moisture rententive for the tomato plants I happened to use it for. I thought I had lucked into a good deal when I got a couple of busted bags for half price ... but the plants in that mix withered up similarly to yours, but not exactly the same color or pattern of disorder. But the mix always seemed saturated. My other potted tomatoes never had a problem all summer even though I watered them nearly daily and at the risk of overwatering ... but they were in a very porous homemade mix and never showed the least sign of what we're talking about here. So, I'm really no help with regard to the possibility of over watering. Personally, since your plants are showing that funky off-color on the leaves AND some of the stem tissue ... and since there seems to be some leaf distortion going on there too ... like a little roll while there's still some greenish color left ... you may want to take some examples of leaves to your county extension horticulturalist. If you do, take some healthy leaves, some that are just starting to show the disorder, and other foliage AND some of those discolored stems in various stages of dying and death so she or he has enough evidence to make a determination whether you're dealing with a fungal or bacterialogical agent or some other thing we all may be missing here.

I doubt cutting off a truly rotted root will harm a palm, but on the other hand, there rarely is a need, either.. .rot does not tend to travel up roots in palms. I would recommend 'play it safe' and generally leave palm roots alone.. .only time I ever cut palm roots is if I am going to transplant a palm that has been in the ground a while and is healthy and established... then it can tolerated being root pruned (though usually not all around the entire circumference at once). Helps decrease the size of the root ball (though will increase the density of the root ball) for eventual digging up and moving. Also note how crammed-packed the palm is in the root ball.... amazing but palms seem to do very well with cram-packed roots and that is the time to move them up to a new sized pot... does not seem to set them back at all to be so crammed, unless there literally is no soil left in the pot.

What a nice plant otherwise... Yes to what breton said, check the heat on the windowsill...also, I would take the pot out of cache pot to make sure there isn't any water sitting there. The pot plant is in is sitting very tight in cache pot, could it be creating too much humidity around the pot? For sure there is no air circulation; set the pot on something to elevate it to improve the air flow. What is it potted in - if peat (as most growers use it), check if it is very dry - peat is hydrophobic and once it dries out too much, very difficult to re-wet. I suspect that may be the case, you said ..."the root system is very tight in the soil"...if that happened, water will not penetrate the soil at all, just slides around and stays dry, and the roots are not getting any moisture. Just few things to consider -

A few hours of LED light each day is clearly not enough replacement for plants (like echeverias) that crave full to shaded sunlight. Mine winter with grow lights up to 8-10 hours a day on a timer, even that is not enough to replace what natural sunlight provides. I set them about 2-3 inches from the actual light bulb, so if you can, adjust your lamp closer to the plants. If you are worried about overwatering, get a small fan to ventilate, and make sure the water doesn't sit in the bottom. Plants wise, your plants are looking fine. As crenda mentioned, flowers wilt and dry away. The most important things to keep watch are how the leaves grow. Healthy roots and leaves = healthy plants.