Hi, I just ran the two new AMR tutorials - `BA.05_AMR` - `BA.06_ErrorEstimator` and the output was not great. While `BA.05_AMR` issues warnings of the following kind ``` loadbalancing with allow_split_siblings disabled may result in bad load balance! ``` `BA.06_ErrorEstimator` additionally only returns NaN for the estimated errors: ``` [0][INFO ]------(0.028 sec) ||e||_L2 ≈ eta_j = -nan [0][WARNING ]------(0.029 sec) loadbalancing with allow_split_siblings disabled may result in bad load balance! [0][INFO ]------(0.119 sec) ||e||_L2 ≈ eta_j = -nan [0][WARNING ]------(0.121 sec) loadbalancing with allow_split_siblings disabled may result in bad load balance! [0][INFO ]------(0.474 sec) ||e||_L2 ≈ eta_j = -nan [0][WARNING ]------(0.494 sec) loadbalancing with allow_split_siblings disabled may result in bad load balance! [0][INFO ]------(1.998 sec) ||e||_L2 ≈ eta_j = -nan [0][WARNING ]------(2.364 sec) loadbalancing with allow_split_siblings disabled may result in bad load balance! [0][INFO ]------(9.343 sec) ||e||_L2 ≈ eta_j = -nan [0][WARNING ]-----(15.924 sec) loadbalancing with allow_split_siblings disabled may result in bad load balance! [0][INFO ]-----(56.370 sec) ||e||_L2 ≈ eta_j = -nan ``` this is of course something that needs fixing. Also I think it would be better, if the tutorial does not report warnings, especially as the option in question seems not to be mentioned in the tutorial, so far. Tested with Clang 15.0.7 (debug mode) and GCC 11.4.0 (release mode).