It runs successfully but takes a very long time, the restore job runs much longer as well, when compared for the 1st secondary.

I think I may have pinpointed the issue, the monitor instance for our configuration is on the 1st secondary, the 2nd secondary can't connect to the 1st secondary and therefore the monitor instance is not being updated with the last_copied_file etc.. for the 2nd secondary and I think this is causing the copy job on the 2nd secondary to scan the entire directory each time it runs.

Could this be the case?