After upgrade to 12.22 ftp does not work

After installing the upgrade, ftp no longer works. If I select a file and delete it, Opus seems to delete the file, but if I refresh the display, it is still there. If I try to copy a new file, or overwrite an existing file, I get the error "Access denied (5)". I opened a ticket with my hosting-provider and all they will say is that these problems mean I am using an "outdated" ftp client. What ever the heck that means. How can I figure out what is going wrong here? Before the upgrade everything worked perfectly.

Try disabling any firewall or antivirus software on your machine, or whitelisting dopus.exe in it. Does the problem still happen then?

Windows Defender has been causing problems for one or two people due to the code-signing certificate being new in the new version. (It should trust the new certificate more after it has seen it more, but that takes time.)

I don't know of any other changes from 12.21 to 12.22 that should affect FTP, so my guess is that it's happening because of antivirus/firewall or similar software.

Defender seems to have gotten confused by the Opus upgrade from v9 to v12. There are two entries in the white-list:
I deleted both of them, and added a new one. Unfortunately, it doesn't help. I forgot to mention, copy from the remote directory to my PC works fine. I managed to use synchronize to copy 15,000 files from the site to a local drive.
Is there any logging in Opus I can use to troubleshoot?

Found "logs" in the menu... This is what I see...
200 Type set to I
227 Entering Passive Mode (185,41,125,51,203,3)
150 Connection accepted
550 can't access file.
It really looks like the problem is with my hostng-provider. They've done something that broke this.

It could be the hosting provider, but it may also be a firewall blocking the data connection.

It could also be the site settings in Opus.

This has a list of things to try: