Samba default implementation for NTIMES VFS verb (vfswrap_ntimes, source3/modules/vfs_deatult.c) used to support easy 'update mtime/atime times to current' semantics (the same way as utime() does). Still new code (added for handling create_time?) doesn't check ft for NULL before use, so SIGSEGV happens when trying to use this feature from VFS module via SMB_VFS_NEXT_NTIMES.

P.S. vfswrap_ntimes checks ft for NULL but too late.

The fix for this issue can be done like this:
--- source3/modules/vfs_default.c
+++ source3/modules/vfs_default.c
@@ -868,6 +868,7 @@ static int vfswrap_ntimes(vfs_handle_str
        goto out;
    }                                                                                                                                

+   if (ft != NULL) {
    if (null_timespec(ft->atime)) {
        ft->atime= smb_fname->st.st_ex_atime;
    }                                                                                                                                
@@ -888,6 +889,7 @@ static int vfswrap_ntimes(vfs_handle_str
                &smb_fname->st.st_ex_mtime) == 0)) {
        return 0;
    }
+   }

 #if defined(HAVE_UTIMENSAT)
    if (ft != NULL) {