Holy shit I was just looking at your logs yesterday, sort of. I raided with your guildie Pypo one night a few weeks ago, he joined my weekly pug. He basically complimented my DPS on Mistress and I was feeling nostalgic, so I was looking at his logs and saw your parses in there and took a look because we're both shadow priests and yeah.
Anyway unfortunately I'm not very good at reading logs to identify rotational issues. I will say that yeah your gear is pretty awful. The right leggos is a pretty big deal, belt and Sephuz, and your haste is a good 10% too low, which is gigantic. I know you don't control what drops for you, but that's a big part of your problem. Not all of it, most likely. But a lot. You did 811k on your July 11th Goroth, which parsed in the 57% percentile. That isn't that bad. That tells me that the potential is there, and personally I think you just need practice. Knowing exactly what button to press and when, and where to stand, and what you're going to be doing in the next 5-10 seconds. It's a hard spec to do well with. It's also likely that the spec is wildly different from what you're used to, whenever you played last. The Mindbender timing thing that you seem to have already fixed is a big big deal too.
Couple things: you speak of a shadow priest dot bug, but I'm not aware of any such thing. What are you experiencing, exactly? Also, it's not 100% accurate to say that Void Torrent should be used on CD, as in the first thing you do every Void phase. That's how guides have been written this tier, but some very high level shadowpriests have been waiting for later into the phase before Torrenting, not just because it gives more ticks of Torrent but because you're extending the phase by longer that way. The idea goes that the insanity decay delay mechanism of Void Torrent is better used when the decay is fast, especially if you have your Mindbender up and refreshing insanity. I myself have been experimenting with waiting until about 20-25 stacks before Torrenting, and I've found that I can achieve 2-3 extra seconds of Voidform, on average, that way. I average about 53-55 stacks, often reaching to like 58 if I do everything well. My best yet was a 61 second voidform, mostly because Heroism was busted at about 25 stacks, so I had it for the higher stacks. I must've also had good tentacle and apparition RNG. I'm sure a better spriest could do even better.
Ultimately the "correct" timing for VTor depends on how long the fight is going to be. If the exact fight length will allow for an extra VTor at the end if you bust it immediately, then that's the right decision. If you won't get an extra if you do that, then it's better to wait. But that's a super high level tactic that only works if fight length is predictable, which usually only happens in really strong, like 6/9 mythic guilds on their weekly plowing through of Heroic, fishing for titanforged crap.
Anyway, tell Pypo I said hi! He was cool.