Thanks for the great input Beminetonight!
FYI, there's also a YouTube playlist regarding the PN5180 I've perused occasionally but most of it goes way over my head (https://youtu.be/_qUS_QvrqGU?si=xfVKhwUoJ93ABsLI).
Regarding the level shifter, I'm at a loss for what I'm supposed to be using. With my original set up, I was using a TXS0108E but was unsure of how to wire up the OE pin and had also received some feedback on this forum that it may not be reliable for this application. That's why I switched to my current level shifter, no idea if it's appropriate or not, was just trying to copy Trappmann's. In the video mentioned above, a different type of level shifter is used but I'm unsure of what model its.
Based on your advice, I used the PM5180 example and was successful! The BAUD rate was different than other example but I was able to have the serial monitor recognize two different ISO 15693 cards. I did however have a similar issue to you in that the system locks up after looping the commands a few times and requires a hard reset to start working again. I'll try to insert a delay later this evening to see if that helps - again, I have no idea what I'm doing.
My end goal is to identify and store a 16 digit numeric code tied to the ISO card as well as turn an LED from green to red and back with each swipe. This will be used to check tools in and out of a workstation while retaining identification of the user that performed the check.
Will update based on my results. I'm now suspecting my initial setup using an Arduino nano and the TXS0108E may have been working all along.