FTP protocol always uses separate connections/ports for data transfers. There's no way your other machines can use 990 port only.
Make sure this is not an active/passive mode difference.
Please read https://winscp.net/eng/docs/ftp_modes

Hello!

I have 4 servers across 2 environments and my "new" prod seems to be using the data channels on separate ports but the other machines (legacy prod, legacy dev, new dev) are only speaking on 990.

All are using the same version of winSCP, same INI, but legacy is Win2012 and new are 2019. Again the new dev box is a mirror of the new prod and there is no AD/AV difference between them.

Anyway it just looks fishy to me that the other machines are using 990 only for all traffic over FTPS but my new box uses 990 and is attempting to communicate on a 51xxx port. My theory is it's something in Windows but it works on the dev 2019 server.

Any help would be appreciated. Tried latest version of Winscp too.
Thank you!

p.s. please don't read into the DEV label. Again their mirrors and in the same OU in Active directory right now, same policy/AV/etc. I'm using wireshark and several other tools to watch the traffic as usual.