using on DH and Shaman, it always interrupts the casting. Tried all lines with [nochanneling,combat] except the Beam.
Example:
/cast [nochanneling,combat] Chaos Strike
/cast [nochanneling,combat] Blade Dance
/use [combat] Heart Essence
/castsequence [nochanneling,combat] Chaos Strike, Blade Dance
Though still interrupts it the moment it goes off, anyone got a solution for this ?
This is the case with azerite beam and also the rustbolt trinket as they have 2 cast times. There is an initial cast followed by a channel; it is in between this transition from pre cast to channel is when it is interrupted by your next move queued up in the macro you are running.
The only way I have found to prevent the interupt is by having focus beam or the trinket use on a modifier which when held until the channel time is completed prevents interruption.
I cannot get modifiers to work for me in macros; there is an exteral keybinding not in wow (as I have removed all known bindings in wow) allocated to my cntrl, shift and alt buttons so I get around this in a very lazy way my main sequence the macro I set to the number 3 I then allocate moves that should be on modifiers if they worked for me to shift-3 alt-3 and cntrl-3, for example my eye beam is on cntrl 3 and my azerite beam is alt3 works like a charm 
This double cast thing is not something GSE can code around as Blizzard simply doesn’t allow it. This is a WoW Macro problem that GSE has exposed.
Best solutions are use a mod key or manually control it. The manual control is how a blizzard expects it would be used.
mod key is best solution so good so far