Ok, I know there have been some issues with textures, shadows, and other similar things on those 7800/7900's, but you shoudn't be having that kind of an issue.
Step 1 : Exclude your game client and save folder from security software. If you say "I don't have any", you have Defender and it must be excluded. I cover this in detail in the Support FAQ thread that is Pinned.
Step 2 : After you have fully excluded the client, now validate the files three times. Once almost never finds everything, and twice isn't much better.
Step 3 : Reboot your computer. I would recommend doing a full hard shutdown and power drain if you haven't in a while.
Step 4 : Back up your save files to another location. (File locations are in the Pinned FAQ thread.)
Step 5 : Nuke everything. The Blue banner at the top of this page has instructions. Want to be certain that everything is fully reset.
Step 6 : Try these video settings. I'm on an R9 3900X with 32GB RAM and a 6800XT. I average well over 100FPS at 1440p all the time.
Step 7 : Try again on a fully fresh map/save. This will rule out any data corruption from previous worlds.
If that works, then you can try restoring previous save data and see how it runs.