It is related to the hiding of the status bar. It later doesn't set the next page size correctly.
You can use this code to first return the status bar and only then show the page:
B4X:
Private Sub timer1_tick
timecnt = timecnt - 1
If timecnt=0 Then
Log("time is over")
timer1.Enabled=False
Dim no As NativeObject = Main.App
no.RunMethod("setStatusBarHidden:animated:", Array(False, False))
CallSubDelayed(Me, "ShowNextPage")
Else
Log(timecnt)
End If
End Sub
Sub ShowNextPage
ShowmainModule.Show
End Sub