Lag with Vessel of Vinktar and Pathfinder

I'm using a cast on crit build (Cyclone, CoC, Blade Vortex, Ethereal Knives, Bladefall, Inc. Crit Strikes) that normally doesn't lag much, if at all. I have a character both on Standard and on Perandus that uses this setup combined with a Vessel of Vinktar (legacy version in Standard). In Standard, as well as the entire Talisman league, the Shadow character doesn't lag while using Vessel of Vinktar in any situation. However, my Pathfinder has extreme FPS issues when I use Vessel of Vinktar against a large pack.

As an example, if I cyclone into a large Perandus pack without Vessel of Vinktar my FPS might briefly spike down to 35-45 at worst. But using Vessel of Vinktar as a Pathfinder and cycloning into a pack will drop my FPS to 10-20, and I've seen single digit FPS using it before. This is easily reproducible, merely attacking enough monsters will

For the Ascendancy nodes, which seem to be causing this, I have the Master Surgeon line and Master Herbalist as a Pathfinder. The character I've tested this with is Fenviri in Perandus League. I haven't tried other Unique flasks yet, so I'm hoping it's not something related to Master Surgeon in conjuction with them.

TL;DR: Vessel of Vinktar creates a lot of lag against a multitude of foes, when used in conjuction with Master Herbalist and/or Master Surgeon.

Edit: It's not just FPS lag, it's latency AND FPS lag. My latency spikes really high in both Predictive and Lockstep, as well as the FPS dipping (and stopping, sometimes!) in both modes. There's something seriously wrong with Vinktar combined with Pathfinder.

Additional Info:

I've been trying to pinpoint exactly what about this setup is generating SO much lag. I've determined it's not exactly FPS lag, but an absolute shitload of information being sent from the server. Enough that it lags in predictive as well as Lockstep. The lag doesn't have to do with my cast on crit setup at all; after having tested using Whirling Blades (and I'm sure any Hit will do the same) through a large pack with Vinktar up, it still lags quite a bit.

I also tried replacing my 20% Phys-> Lightning version with a +lightning damage to spells version of Vinktar, but if anything the lag is worse. I tried speccing out of Master Herbalist as well as Master Surgeon ascendancy nodes, and didn't notice any improvements.

Thinking it was the Leech that was perhaps creating so much lag, I tried an Atziri's Promise, but Atziri's Promise doesn't change my FPS at all in packs; it was immediately noticeable compared to Vinktar.

I have a sneaking suspicion it's actually hitting a shocked mob with Vinktar up that's generating the lag, but I have no idea why.

I'm having this exact same problem, only my computer isn't as good. I drop below 1 fps against big packs and it's making it literally impossible to play with this flask in PHC... can we get any progress on this?? :(

E: two other people dealing with this issue https://www.pathofexile.com/forum/view-thread/1640712