This is a GREAT question! What does high "tech" mean? It means more energy in the system. More energy (in the form of light) drives photosynthetic rates. Those rates are then realized by nutrient availability. Of all of the nutrients, phosphate has the largest impact on growth rate + size. So, you pelt it with light, you give it all of the fuel with phosphates, and all the plant has left to do is grow. If any nutrient is deficient, it grows deficiently. So we give it all in excess (generally speaking) or just enough and induce a limitation via minimizing phosphates/nitrates - never CO2.
You are not referring to "easy" plants, you are referring to slow growers. Those plants are good long-term condition tank indicators. This means that your anubias that is unhealthy, is probably reflecting tank conditions from a month or so ago - has anything happened? An ammonia spike, a rescape, a change of flow-distribution, a change in CO2, a change in dosing regime? Was it just added recently?
If you lack water column dosing, maybe your substrate has run out due to the high light demand? This is unlikely - but still.
But what we are missing is photo oxidation. You mention something about the plant transitioning into "red" and then it died ... perhaps your PAR is so high at the surface of that plant that it degenerated its chlorophyll (that makes the plant look green) and revealed the pigments beneath - that is why plants turn red under high light ... it's not just nitrate limitation - at that point, it couldn't keep up and you melted it with light. Certainly that is possible - but only at high, high PAR. And I am running my a 65 gallon tank with java and anubias close to the surface with 2x freshwater AI primes at 100%, so it should be higher than that value.
I am assuming you dose EI and have good flow + distribution ... so why pinholes? Photo oxidation. Or not - we do not have any details of the tank layout etc.
Throw that anubias in a shady region and see if it comes back.
Why no growth yet? Has it throw roots? Has the rhizome changed? Growth is not always leaves.
Please give some more details so maybe we can get to the bottom of this!!!