CoC and Efficiency 2 support gem

ill gues support Efficiency 2 not working for spell in coc
and seems blood mage passive Sanguimancy not working to

how do you tested it? I just checked it and efficiency 2 works and reduces life costs.
You should use Blood Magic passive anyway to get rid of limiting mana costs but Sanguimancy shows me life and mana costs on spells, how does it not work properly?
There are other bugs with CoC and certain support gems like seen in my latest bug report but this here doesn't seem to be bugged to me.

The point of how I noticed this and why I started doubting how Cast on Crit works:

I have around 800 mana.
According to the tooltip, the spell I’m actively spamming costs 31 mana, and the triggered spell costs 50, so 81 mana total per trigger cycle.
My mana regen is around 120+.

With those numbers, it should take a noticeable amount of time to actually drain my mana pool. However, during boss fights, there are moments where my entire mana pool gets completely drained in about 1 second. At the same time, there are no visible extra spell animations or damage spikes that would explain such a massive number of casts happening instantly.

This only happens when I am hitting enemies, which strongly suggests that the issue is related to the triggered spell, right?

Now, if we look at the life cost side: the triggered spell has a 120 life cost.
If I am losing 800 mana in one second, that would mean
800 / 50 = 16 triggered casts.

That would be
120 × 16 = 1920 life.

I have around 4k HP, so I would definitely notice such a life drop — but there is no noticeable life loss at all.

What’s interesting is that if I check the skill information by hovering over the gem without the combined tooltip, it shows a mana cost of ~300, which actually matches what I’m observing in practice: my mana can drop to zero in just a couple of casts.

This does not happen 100% of the time, which makes me suspect that sometimes, when the spell is triggered, Blood Mage passives, cost efficiency from the tree, and even the “less cost” support gem are not being applied at all.

That’s why I decided to post this on the forum so the developers can take a look at it.
For reference, the triggered spell is Thrashing Vines.

And just to be clear: I’m not asking for build advice or suggestions on how to play — I’m only reporting what looks like inconsistent or incorrect cost calculation.