I as well have been having major issues since the last patch.

Intel i7-7700k 4.2ghz
32GB GDDR4 RAM
Gigabyte Aorus GTX 1080ti 12GB
EVGA Supernova 1100W PSU
Alienware aw3418dw

A couple of patches ago I could run this game smoothly at 110+ fps consistent at 3440x1440 in borderless windowed (running a second monitor on the side, 1080p). As of the last patch my game will instantly spike to 100% GPU utilization in task manager and suffer severe stutters in game. At one point I loaded into Ul'dah Steps of Nald and if I am looking up the steps out of the spawn room my game looked like a powerpoint slideshow, but turning away from the steps returned to normal performance. The only way that I have found to rectify this problem is to drastically neuter my game visuals (removing Stormshade, turning off HBAO+ Quality, turning off high quality model for shadows, limiting FPS to 120, running in fullscreen). Even now, it is not perfect and I will still get an occasional hiccup. After playing for an hour or two it still rises up to 100% GPU utilization and is prone to crashing.

I have rolled back my Windows 10 to prior to the last update. I have uninstalled all GPU products (Aorus GFX Engine, MSI Afterburner). I have performed a clean install of my GFX driver. Powered down and deep cleaned and released residual charge from the rig itself. Performed a clean-boot and ran only FFXIV on top of system processes.

I do not have this issue on any other game that I play/have installed. This includes Overwatch, ESO and Destiny 2.

My belief is that as of the last patch there is a major memory leak issue that needs to be found and addressed.