Spell Timers not working for some Spell Effects
 

If I have Thieves Guild cast on me then Organized Crime will show on my Spell Timers window, but if I'm in group with a brig and he has cast it on another group but still proccing it for my group, it won't show up, even though I can see it on the Spell Effects.

The same applies with the SoD celestial familiar 5% Base Damage proc Ethereal Buildup - it will show in Spell Effects but not Spell Timers.

Anyone know why this is and if there is a way to make it work?

It's also not working for the Affix of the Infernal Tyrant proc "Infernal Ascension".

Does anyone know why these procs do not appear on Spelltimers window or if there's a way to add it?

The Maintained Spell Monitor can only monitor effects that appear in the Maintained Spells window. Icons in the Spell Effects window cannot be monitored.

If an effect appears in your Maintained Spells window but is not showing up in the monitor, mouse over the maintained icon and make sure the effect name in the tooltip is exactly the same as in your setup. Sometimes the effect name is totally different from the spell that was used to cast it.

And finally, anything beyond 30 maintained effects won't appear in the Maintained Spells window or in the monitor. You can use Spell Filtering to hide unneeded maintained icons, which will make room for other effects you want to monitor. The DarqUI Help tab in the in-game Help window has info about that.