FTP freezes on multiple file/folder transfers

Opus FTP is great for single files, but I am constantly having issues when trying to FTP multiple files/folders either up or down. It'll do one or two and then just freeze, and I have t abort then start over. IN fact it's so bad I usually open Filezilla now for such operations. I've had this problem with Opus FTP for ages, and on different computers…. can I really be the only one affected by it?
ta...

What does the FTP log say when it happens?

Is it only with particular sites or server versions?

Thanks for replying.

It runs along fine, then just hangs... eventually I get (in the logs)

Timeout on Command 1018.
Connection closed

It tries then to reconnect, and I'll get (after a bit of bumpf)

--> REST 34051
350 REST command successful.
--> RETR [filename]
550 The REST value is beyond the end of the file.
User Aborted Transfer
Connection closed
FD_CLOSE - WSAECONNABORTED: Software caused connection abort

The "User Aborted Transfer" is when I get a popup MessageBox saying:

"An error occurred copying
Access is denied. (5)" - Retry, Skip, Abort.

I nearly always use this from/to Windows machines (my dev machine is W10, the server is Windows Server 2012). Occasionally I'll connect to a Linux box, but tbh I can't recall offhand if this is a problem with those or not...