There is a circular dependency when terminating an inmemory file system.  The connection requires the session to then call filesystem terminate. The file system terminate then eventually calls __im_handle_remove, which requires a variable from the connection, see here:

    bucket = im_fh->name_hash & (S2C(session)->hash_size - 1);
    WT_FILE_HANDLE_REMOVE(im_fs, im_fh, bucket);

This ticket involves finding a method to remove this weak circular dependency.