Invisible Garuda HM

Hello, I've run into the issue in my title now on a few occasions.

During the Garuda HM fight, she disappears as usual, but at times she fails to reappear on my screen. This can happen both during the first phase (rock piles) or in the second phase (the two adds).

I'm not sure if it's related to lag or what, but it makes the fight very annoying. Luckily it hasnt happened on my tank yet, only on my dps.

My PC is.

i7-2600 3.4GHz
ATI Radeon HD 6870 (13.9)
8gig RAM
Win 7 64 Home premium fully updated
DX11
24MB internet ISP Bredbandsbolaget Sweden.

I've tried this with and without different boosting program, she dissapears either way.