I have tried the following solutions, by setting up UVs and setting the Tangent Style to Compute from UVs, to no avail.
https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=20693&highlight=&sid=3fada40b05c9700ff2f49b64d41b569b [sidefx.com]
http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=31378&sid=330543f06b02c0155095010dffb60f51 [sidefx.com]
In fact, nothing changes when I update the tangent style to anything.
Here is a picture of the UVs, and of the rendered image. It works okay but not great on a sphere, but has clear discontinuity artifacts on my object.
Any ideas as to what the issue might be?