That happens when the material is partly raster-based rather than fully procedural: the bake captures the source images, and they tile only if they were seamless to begin with. Switch Tile mode to Edge Blend with a border of about 5-10% of the resolution. If the seam survives that, use Mirror Tile — it is seamless by construction, at the cost of doubling texture memory. Both the bake and the tile-correction report print a measured wrap-seam error, so you can see whether the change actually helped.