@DavidCarlisle, I found it.
Underfull \vbox (badness 3503) has occurred while \output is active
\vbox(658.28194+0.0)x426.79135, glue set 3.27487
.\glue(\topskip) 0.0
.\hbox(14.2795+4.24133)x426.79135, glue set 3.19337fil
..\hbox(0.0+0.0)x0.0
..\T1/ntxtlf/b/n/20.74 3
..\T1/ntxtlf/b/n/20.74 .
..\glue 20.74
..\vbox(14.2795+4.24133)x384.1096
...\hbox(14.2795+4.24133)x384.1096, glue set 8.41257fil
....\hbox(0.0+0.0)x0.0
....\T1/ntxtlf/b/n/20.74 F
....\kern-1.14072
....\T1/ntxtlf/b/n/20.74 o
....\T1/ntxtlf/b/n/20.74 r