To be clear, this sequence of calls crashes the vpp:

vat# memif_create
created memif with sw_if_index 1
vat# want_stats enable
vat# sw_interface_set_table sw_if_index 1 vrf 1
vat#

or

vat# memif_create
created memif with sw_if_index 1
vat# sw_interface_set_table sw_if_index 1 vrf 1
vat# want_stats enable
vat#

It seems the type of the interface is not important. It happens only for vrf > 0.

vpp# sh ver
vpp v18.04-release