Unfortunately, I don't think there is enough information provided to help diagnose the specific cause of the issue (the general cause is likely to be memory corruption). The following 3rd party C-extensions are in use:
A memory issue in any of those could cause a segfault in append_features. If it is possible to disable the use of all or most of the external C extensions and see if that makes that problem go away, that would be one way to go about diagnosing the problem.