Infrequent incorrect fractional solution with very low accuracy

[PetterS]

When running the largest instance (24) from http://www.schedulingbenchmarks.org/nurse.html and --objective_change_before_fixing=100 the following happens after a few solutions (many hours):

Error: Assumption failed: abs(fixes_for_member(p)[c] - fractional_solution(p, c)) <= 1e-3 in compute_fractional_solution (set_partitioning_problem.cpp:539). Fix state does not correspond to fractional solution. A column violating the fix state may have been added.

Stack trace:
12: ??? + 0
10: minimum::linear::colgen::ColumnPool::size + 9484
9: minimum::linear::colgen::SetPartitioningProblem::compute_fractional_solution + 455
8: minimum::linear::colgen::SetPartitioningProblem::fix_using_columns + 121
7: minimum::linear::colgen::SetPartitioningProblem::fix + 74
6: minimum::linear::colgen::Problem::solve + 396
5: ??? + 0
4: main_runner + 141
3: ??? + 0
2: ??? + 0
1: BaseThreadInitThunk + 20
0: RtlUserThreadStart + 33

Everything works well with --objective_change_before_fixing=10 for which 10 solutions can be computed.