The stock LPN client for Mesh SDK v4.0.0 throws NRF_MESH_EVT_SAR_FAILED when replying to a publication set message via a friend node.
All code, reproduction data and log output is here: https://github.com/siriobalmelli/nrf_mesh_4.0.0_lpn_SAR
I also tried to implement the suggested answer from this thread:
... this did not work, see this commit:
Have you made any modification to the LPN example?
I'm not sure if this will make any difference but could you also try using our nRF Mesh app instead of the BubblyNet app? Any difference?
It seems like your mobile is still connected to the LPN via GATT even after LPN has established the friendship (Note that, after the provisioning and configuration, the mobile remains connected to the node, unless you disconnect it explicitly). There is a known issue with LPN that when LPN is in friendship with Friend Node, a connected GATT device receives packets encrypted with the wrong encryption key. Therefore, the response to the Model Publication Set is not understood by the mobile app, and hence it fails.
Try to configure the LPN node via Friend node. Disconnect the mobile app from LPN, and explicitly connect to Friend proxy node. Then try configuring the LPN node via Friend node. This should work.
Please see https://github.com/siriobalmelli/nrf_mesh_4.0.0_lpn_SAR/blob/master/README.md#reproduce-mesh-lpn-friendship-sar-bug step 2.
I am making sure that GATT is not connected:
1. On BubblyNet App by clicking "disable proxy" after provisioning
2. On nRF Mesh App by manually changing to the light server as a proxy so messages *must* go through LPN