wget throws “Is a directory” error

I need to download about 10,000 files from a HTTP server. I am using wget. It works. This command created a subfolder 192.168.1.173+8080/files with about 4,000 files, after which I believe the HTTP server crashed.

wget -r --no-parent http://192.168.1.173:8080/files

I restarted the HTTP server. I would like to restart the download, and skip all existing files, but if I run the same command I get an error.

$ wget -r --no-parent http://192.168.1.173:8080/files
--2025-06-11 12:05:10--  http://192.168.1.173:8080/files
Connecting to 192.168.1.173:8080... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: /files/ [following]
--2025-06-11 12:05:10--  http://192.168.1.173:8080/files/
Reusing existing connection to 192.168.1.173:8080.
HTTP request sent, awaiting response... 200 OK
Length: 1623291 (1.5M) [text/html]
192.168.1.173+8080/files: Is a directory

It seems related to the folder already existing. I tried --nc and -N but to no avail.