:( after doing the quest to retrieve the staff of Magnus, the infinite concentration spells ability seems to have been reverted, is there anyway to avoid this !?!

It's the wisp mother in Labyrinthian.  The 'death blast' from her or a wisp will break the effect unfortunately and the only cure is to get the potions and reacquire the atronach stone.  It can be avoided by killing them at range.  Same with any wisps you encounter in the wilds.

Thanks for the quick reply, ahh ok I may just avoid them altogether, I wonder what it is that affects the ability in this way ?

No idea.  The only other time I lost the effect in two playthroughs was when I was at the summit of apocrypha.  Might have been Miraak's tentacle explosion.  Anything that alters your magicka, potions, fortify magicka enchantments, etc. will also break it.  Interestingly, being a vampire reduces your magicka in sunlight but doesn't break the concentration casting.

Hey Mason! Just wanted to know my game seems to have fixed quite a few glitches the ultimate atronach glitch for etc. (it's probably one of my mods) but anyway is this build worth it without the infinite casting should I play my demonhunter and call it a day?

Incidentally, if anyone is interested the ultimate atronach also works with high elves if you use 21% followed by draught of the healer.  You get 218 magicka and unlimited concentration casting.

Also since I play with the Skyrim Redone mod, which replaces the voice of the emperor power with two powers that buff followers with ten minute cooldowns. Since I travel alone unless I have to (looking at you Serana!) these abilities are completely useless to me and my Seraphim has a giant hole in her defense. I think I will change the race to nord seven seconds of invincibility is much more useful

Mason, Great work on this build man i'm really impressed.

One problem though that is to do with the Ultimate Atronach glitch, It appears that the popular skyrim mod "SkyRe" fixes this exploit and therefor I am struggling to play this build without unlimited concentration spells, If anyone on here has any idea on a fix for this or how to bypass it would greatly appreciated!

It appears Skyrim Redone does fix the ultimate atronach stone exploit.
I am having the same issue, If you find a way to bypass this I'd really appreciate the help man!

You could just add in some magicka boosts when you level up I myself used 3 health 2 stamina 2 magicka with the atronach stone and had no problems, I also specialized in fire magic to cut down on the spells clogging up my favorites menu. If you have problems casting spells you could just add more magicka when you level up or use magicka increasing items. As far as I know the ultimate atronach glitch is fixed in Skyrim Redone so can't help you there