Hello all,
We're well aware of this issue and are currently not aware of the root cause. We'll be looking into it over the coming weeks however it's going to require a long and repetitive process of elimination. Thank you for your patients.
Thank you for your patients all. I have a status update on this issue.
I spent the majority of yesterday picking apart the pack in order to determine a better understanding of this bug and potentially find the cause. I partially knew the issue was related to SwingThroughGrass - a mod that fixes a nuance in vanilla Minecraft where you hit tall grass before hitting the mob in front of you. However, it was not the sole mod at cause here as the mod on it's own did not produce this issue.
After many hours of removing mods and reloading the pack, ensuring that I was through and consistent with all my tests, I came to the conclusion that the second mod involved was /dank/null and shortly confirmed it by placing just /dank/null and SwingThroughGrass in a pack together by themselves.
Therefore, I've spoken with p455w0rd the author of /dank/null who will be taking a look into the root cause of the issue soon. I've not yet spoken with the author of SwingThroughGrass as I'm unaware if they're still active within the community. However, the issue has been reported to both mod authors in a professional and detailed manor.
While myself or anyone else isn't aware of the precise issue and where the cause is this was the most accurate determination I can make.
Thank you all for continued support in reporting issues as well as the patients with this issue and I hope that we'll have it sorted soon.
SnowShock35.