Hello Christophe,
your problem is caused by the very large simplification of the model, large differences in the resolution of the original and simplified model (as you can see in the screenshot) causes that the whole texture is much sharper than the texturing of simplified parts. Large simplification of the surface causes small yet significant movements of the surface and therefore the discrepancies between the textures. Large difference in surface detail results in the visible seams on the edges of individual parts.
simplified model (left side) vs. original model (right side):
Difference in texture partial - top, whole - bottom.
Based on the experience we generally recommend to simplify the models max 10 times to preserve a detail that does not cause problems in the texture. Therefore, we recommend you to use previously mentioned workflow: Reconstruct -> 10x simplify -> texture -> export -> re-topologize the exported model -> re-project the texture from the exported to the re-topologized model.