Hi and welcome to the Forum! It always helps to tell us where you are located. There are hardly any garden questions that can be discussed without regard to location/ climate. I never heard of murraya, so I looked it up. It seems to be a plant of the southern hemisphere. Wiki says "It is distributed in Asia, Australia, and the Pacific Islands. The center of diversity is in southern China and Southeast Asia." Can we assume you are in one of those places? Or maybe SoCal or other very southern parts of US?
When you were talking about how you feed it, you said sesol. I couldn't find any results for that, but maybe you meant seasol, seaweed extract? That sounds like good stuff.
Looking all this up, because none of it is familiar to me, I found that Seasol and PowerFeed are from the same company:
"What is the difference between Seasol and PowerFeed?
Seasol is made from two species of seaweed - Bull Kelp (Durvillaea potatorum) and Knotted Kelp (Ascophyllum nodosum). It is not, by definition, a fertiliser (as it contains only marginal nitrogen and phosphorus levels). Seasol seaweed concentrate is a complete garden health treatment that contains plant nutrients, trace elements, alginic acid and other bioactive compounds. Seasol promotes healthy roots, encourages beneficial soil micro-organisms, stimulates flowering and fruiting and helps plants to cope with stresses like heat, drought, frost and pest and disease attack.
PowerFeed is a fertiliser. It has a fish base which is fortified with nitrogen, phosphorus and potassium. The ratio of which is Weight to Volume N 12%: P 1.4%: K 7% respectively. PowerFeed also contains dynamic soil improvers in the form of humic acids. These compounds work at very low rates and are literally like adding liquid composts to the soil. As well as being a quality fertiliser, PowerFeed is also a clay breaker. It stimulates beneficial soil microbial activity and markedly reduces leaching in sandy soils."
So all pretty good stuff, but feeding every week sounds like too much. I hope you are using it very dilute. 12% N is also quite concentrated.
You have a moisture sensor, so presumably you are watering correctly, but sometimes automated drip irrigation systems keep things too damp too much of the time, especially if you are also getting rain. Yellowing and stunted sounds like lack of nutrients, but since you are if anything overfeeding and since the other individuals in your hedge are fine, that clearly isn't the issue. But looking nutrient deprived in the presence of plenty of nutrients can happen when there is a problem with the roots. The nutrients are there, but the roots that are diseased or damaged in some way can't take them up.
So since I never even heard of this plant, this is all guess and speculation (combined maybe with logical deduction), but my guess would be that your struggling plants maybe have developed some Phytophthora (root rot). This can happen when your soil stays too moist, and is a fungal disease. Symptoms of root rot look a lot like nutritional deficiency, because of the uptake issue I mentioned, but an inspection of the roots system will show the decay of the feeder roots. They may be brown/black, mushy, or even smell bad/rotten.
Murraya is a drought tolerant plant, which means it doesn't do well with too much moisture and needs to dry out some between waterings. I suggest backing off on all the watering and feeding. You may be killing your plants with kindness.
You may need to dig up which ever one is struggling the most. Dig it up with the root ball, damaging the roots as little as possible. Then wash the soil off the roots, so that you can see what is going on. If some of the roots are showing root rot symptoms, prune them off. Then replant, but first mix in some cactus mix or coarse sand or perlite into your soil to improve drainage. Then as noted, slow down on the watering and feeding.
Let us know what you find!