Problem should be fixed by this upstream commit:

commit cd21ae40130b4d1ddb3ef500800840e35e7bfad1
Author: Phil Sutter <phil@nwl.cc>
Date:   Mon May 6 19:09:56 2019 +0200

    ip-xfrm: Respect family in deleteall and list commands
    
    Allow to limit 'ip xfrm {state|policy} list' output to a certain address
    family and to delete all states/policies by family.
    
    Although preferred_family was already set in filters, the filter
    function ignored it. To enable filtering despite the lack of other
    selectors, filter.use has to be set if family is not AF_UNSPEC.
    
    Signed-off-by: Phil Sutter <phil@nwl.cc>
    Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

Note that instead of 'flush' one has to use 'deleteall' command.

Since this issue is not critical, I'm moving it to RHEL-7.8.

Hi, this is fixed in rhel-8, is there a customer request for this to be in rhel-7?
If not I would like to CLOSE/WONTFIX this and direct users to use rhel-8 instead. Let me know what you think.

Andrea, 
 No customer request, it was found when I did qa test.
 I agree with you to WONTFIX it.
 Thanks
Xiumei

Thanks Xiumei, closing according to the comments above.