SQL Server Log shipping standby db stuck restoring
Turns out the log shipping configuration has reverted to NORECOVERY instead of STANDBY.

I think the is that there must have been an open session on the database, SSMS or alike and after a set period the log shipping is configured to revert back to NORECOVERY. The original configuration was did not have the 'disconnect users currently connected' option enabled.

To resolve the issue I simply went back into the original database and selected ship transaction logs and then selected the radio button for STANDBY instead of NORECOVERY