that "bug" it seems to be a really big lag spike but seeing that you have fiber cable with a good down/up its strange.
maybe your ISP doesn't like FFXIV for some reason (I still remember when I had to call my ISP a lot of times to help me with my 10K ping on WOW wich was on their end) try playing at differents hours to see if happens maybe its because your IRL zone is congested when you play at that gives you lag