> When I import the maps to UE4 they come in as one file with the VT icon and I have enabled Virtual Textures in the settings menu.
This is working as intended.
> I then do a basic material and apply the map to the terrain and it looks tiled for some reason, as in the image below.
Sounds like a problem with your UVs? A 5x5 UDIM texture will need UVs in the range 0.0-5.0 in order to cover the full UDIM space. I’m not actually sure how terrain UVs work, but you might try scaling the UVs in your material.
> I have tried the maps with both types of naming AO_1001.png and AO.1001.png
You should be using Name.1001.png, Name_1001.png won’t be detected as a UDIM
> Also tried adding a Virtual Texture Runtime Volume
Runtime VT won’t work correctly when combined with streaming VT (which includes UDIM). Runtime VT will cache the material results, which means you’ll typically end up caching the low resolution streaming VT mips. There’s currently no mechanism for streaming VT to invalidate the runtime VT cache when new tiles stream in (and it’s not clear if this functionality makes sense to add).