Hi All, I'd like to advise you all on how to fix the NPCs becoming invisible and also how to enable the inventory and chatbox to become transparent if you wish to do so, this is for resizeable mode only.

(This only applies if you use RuneLite) So first of all for the NPC and character issue where you or the NPC would become invisible (You character would only become invisible when doing an action from the inventory e.g. Eating food, Drinking potions, teleporting, etc. Equipping items do not have this issue).
What you want to do is to go to your RuneLite settings and fine "Animation Smoothing" and disable this (make sure it's got a red X next to it. Once done, restart your client and this will resolve the issue for the time being.

(this applies to both Vanilla and RuneLite) There is also an issue with the transparent chatbox, inventory and also the side-panel options (I have not found a work around for the side-panels at the moment but if you know how to resolve this, please comment below).
So you go to the settings in-game and then to go Advanced Settings. To enable transparent chatbox you need to click the "Data Orbs" option and this will enable/disable transparent chatbox.
Click here to see a GIF of what I'm on about if you're unsure https://gyazo.com/c7526aa38d678d38ff111ae8101e38e7

Again for the transparent inventory you want to go to Advanced Settings and select "Resizable mode scrollbar position (Currently Right) and this will enable/disable transparency for your inventory.

Big thank you to Miika and a randomer in the CC (I can't remember your name, sorry!)