TLDR: Two rogue based characters while using any form of gun or crossbow are stuck in a reloading loop and cannot auto attack.
So during my play through I eventually came to the realization that one of my characters (Ydwin lvl 15 Mindstalker) auto-attack wasn't functioning (spell/abilities were still working properly). At the time that I had noticed, it was already too late for me to go back and find when and where the issue first arrived (as I save very frequently).
So after being aware of the issue I decided to test a few things such as:
Unequipping the pistol/blunderbuss that I was currently using and re-equipping the weapons to see if that would fix the issue, it did not.
Tried using a melee weapon in the weapon slots they were originally in and swapping them to another weapon set, this didn't fix the issue either.
I tried restarting my game, steam, and my computer. These didn't fix the issue.
I verified my steam game files to no avail.
After I those tests at a solution, I decided to put the weapons, the "Thundercrack Pistol" and "Eccea's Arcane Blaster" to be exact, on another character (my main Assassin also lvl 15) and they appeared to be functioning properly so I figured it was just a character issue with Ydwin. Well, as it turns out, the issue happened again on my main and again I didn't realize it before it was too late. By the time I realized the issue had appeared on my main, she was lvl 17.
*Note - the ability "Conductive Blast" from the "Thundercrack Pistol" still functioned properly it was purely the auto-attack with the weapon that doesn't function.
I decided to test if it was just guns or all ranged weapons. From what I gathered it was an issue with crossbows, arbalests, blunderbusses, pistols, and arquebuses.
Originally, I had Serafen using the two pistols mentioned and he had no issues with them.
I have Maia using "Blightheart" an arquebus and she has yet to have come into a reloading loop.
While trying to look to see if anyone else had come across the same issue, I had stumbled on a forum post about PoE1 that it was a known issue with rogues to get stuck in a reloading loop but there was no info on a solution for the issue.
And noticing that both my main (Assassin) and Ydwin (Mindstalker) are both forms of a rogue I figured it was the same issue as what was happening to those in PoE1. So to me it appears to be an issue purely with rogue based classes.
Edit - If anyone else has run into this issue please let me know and if you have any other info I haven't posted.