probably missing a log backup so nothing for log shipping to apply as far as it is concerned.

run these queries for info

-- error details

select * from msdb.dbo.log_shipping_monitor_error_detail

select log_time_utc,message from msdb.dbo.log_shipping_monitor_error_detail

-- tells you last log copied and restored, primary and secondary server names

select * from msdb.dbo.log_shipping_monitor_secondary

--tells you restore settings

select * from msdb.dbo.log_shipping_secondary_databases

--tells you where database log was backed up to (run on primary)

select a.database_name,a.backup_finish_date,b.physical_device_name

from msdb..backupset a inner join msdb..backupmediafamily b

on a.media_set_id = b.media_set_id

where database_name = 'dbname' and type = 'L'