power strap did not connect to metal 1 in standard cell rows

xiaoyisimonguo

in IC compiler:I did floorplanning, p/g ring, VSS and VDD, then
create_power_straps  -direction vertical -layer M4

then
preroute_standard_cells -route_pins_on_layer M1 -connect horizontal

but I later found that the straps to ring connections are perfect, but straps to M1 VDD/VSS connection was not
there, I did try M4, M6, and M8,

Please help