'Mixer load failed' error message

I have built my own hexarotor coaxial model and I am trying to perform a SITL gazebo simulation. The mixer I used is the one corresponding to the hexarotor coaxial configuration.
The simulation fails and apparently it is due to a mixer problem. I performed a mixer test and several errors arise:

INFO  [tests] RUNNING TEST: loadIOPass
file not found
ERROR [tests] Compare failed: check number of mixers loaded - (mixer_group.count():0) (expected_count:8) (.
ERROR [tests] Mixer load failed with chunk size 6
ERROR [tests] TEST FAILED: loadIOPass

INFO  [tests] RUNNING TEST: loadQuadTest
file not found
ERROR [tests] Compare failed: check number of mixers loaded - (mixer_group.count():0) (expected_count:5) (.
ERROR [tests] Mixer load failed with chunk size 6
ERROR [tests] TEST FAILED: loadQuadTest

INFO  [tests] RUNNING TEST: loadVTOL1Test
file not found
ERROR [tests] Compare failed: check number of mixers loaded - (mixer_group.count():0) (expected_count:4) (.
ERROR [tests] Mixer load failed with chunk size 6
ERROR [tests] TEST FAILED: loadVTOL1Test

INFO  [tests] RUNNING TEST: loadVTOL2Test
file not found
ERROR [tests] Compare failed: check number of mixers loaded - (mixer_group.count():0) (expected_count:6) (.
ERROR [tests] Mixer load failed with chunk size 6
ERROR [tests] TEST FAILED: loadVTOL2Test

INFO  [tests] RUNNING TEST: loadComplexTest
file not found
ERROR [tests] Compare failed: check number of mixers loaded - (mixer_group.count():0) (expected_count:8) (.
ERROR [tests] Mixer load failed with chunk size 6
ERROR [tests] TEST FAILED: loadComplexTest

INFO  [tests] RUNNING TEST: loadAllTest
INFO  [tests] Testing all mixers in etc/mixers
INFO  [tests] TEST PASSED: loadAllTest

INFO  [tests] RUNNING TEST: mixerTest
file not found
ERROR [tests] Compare failed: check number of mixers loaded - (mixer_group.count():0) (expected_count:8) (.
ERROR [tests] Mixer load failed with chunk size 6
ERROR [tests] TEST FAILED: mixerTest

ERROR [tests] SOME TESTS FAILED
INFO  [tests]   Tests passed :      1
INFO  [tests]   Tests failed :      6
INFO  [tests]   Tested assertions : 3422

It appears that I have the set the wrong number of mixers? How can I fix that?