Is there any reason why i would be missing void eruption in the shadow priests rotation..ive confirmed i have the latest version and that its on my bar. However im never asked to use it and just do it myself - once i have void bolt does appear in the rotation. Im not an experience user with Hekili but so far im liking the addon!

It's most likely that you do not have the Cooldowns toggle turned on (see /hekili > Toggles).

If it's not that I have no way of answering with the limited information provided. See the ticket instructions when you click the "New issue" button here.