I've imported a model from a game. It has UVs stretching beyond the image texture included. The texture is designed where the UV maps to a mirrored-repeating texture, but Blender 2.8 only has a "Repeat" texture extension.
This has been solved in the past for an older version of Blender, but the solution given does not apply to Blender 2.8: How to repeat a texture mirrored?
At its simplest, with a UV map like this:
.. which I think is equivalent to yours?
Then all you have to do is put a Math > Ping-Pong node in the way of the X and Y outputs of the UV texture space, on the way into the image:
If you find you need to tweak offsets, scales of the repeat, you may find it easier to wrap Ping-Pong up with something like the 'Triangle Wave' group you can download from this answer.
If you have several different UV maps, then instead of the Texture Coordinate input node, you would use a UV Map input node, to select the right one.
