A DirectX error isn't always actually related to DirectX, I recently had a couple myself which were actually RAM issues.
Quote Originally Posted by Sirkos View Post
[...]
rarely i will notice my GPU doing something weird, like on my screen will have blocky effect and lines going down for half a second, and 1 time textures in game were broken or nonexistent to me.[...]
This certainly sounds like a GPU issue, can you reproduce crashes in other applications when GPU utilization hits 100% to try and narrow down if it's a problem isolated to FFXIV or a general issue with the card?
Does the card handle a stresstest like FurMark?