FTP/FTPS - archive or timestamp comparison - best practices

Hello

We seem to be reading quite a lot of FTP/FTPS (not SFTP) files, I know it probably is a bit oldfashioned but this is our reality.

Now I am facing a few challenges:

FTP/FTPS adapter is monitoring a folder on a Remote FTPserver (30 sec. polling interval), publishes if there is a new file and the OnPublish starts a process (a couple of DB operations)

The FTP/FTPS adapter is set to archive the file to ArcheveFolder on the remote FTPserver.

This works very nicely 99% of the time.

1% of the time I see the an identical file being downloaded with e.g. 5 minutes between. 

I do not want this to happen.

I got a feeling that this might happen because of some work on the server hosting Neuron or the surrounding network but not certain. I know the server is not restarted. 

The explanation could be that if there is some work on the server that interrupts the process then perhaps the FTP/FTPSadapter never gets to archiving the file. 

The remote server could also be the problem: perhaps they are doing work there, which is difficult to get a fast answer about since they have outsourced their IT operations.

And I have started thinking about using timestamp comparion in stead.

So the question is:

Do any of you other Neuron folks have experience in the area and found e.g. TimeStamp comparison to be more stable/precise than using Archive Folder?

The files I want to downlaod all have unique filenames: named from the year+week they were built.