Finally Unchecked (Enable Hardware Decoding For Supported Devices) and I am no longer getting any thumbnail freezes/related crashes. This was also causing video flickering when rendering using my default XAV-C profile. Settings below hopefully this helps some of you out. Oddly enough at least when using a XAVC profile rendering times are much faster when this setting is unchecked.
(Additionally the preview is still buttery smooth as this settings still falls under "GPU acceleration of video processing)