cell delay only have rise triple

[young03600]

Hi,

I found that if I run STA under multi-corner there will have some instances only have rise triple?
Is there any reason that happened?
Thanks.

The following is the case:
under ff_n40C_1v95

 (CELL
  (CELLTYPE "sky130_fd_sc_hd__dfxtp_1")
  (INSTANCE _6427_)
  (DELAY
   (ABSOLUTE
    (IOPATH CLK Q (0.19001253885919475173::0.19001253885919475173))
   )
  )

under tt_025C_1v80

 (CELL
  (CELLTYPE "sky130_fd_sc_hd__dfxtp_1")
  (INSTANCE _6427_)
  (DELAY
   (ABSOLUTE
    (IOPATH CLK Q (0.30703598865751718927::0.30703598865751718927) (0.29855013750667658279::0.29855013750667658279))
   )
  )