Hey Tomasz, good to read you. I hope you are fine and with good health.
I have validated the files.publii.json file using the link you provided an it resulted in a “Valid JSON” message as you can see in this screenshot.
For what is about the deployment method: yes. I am using the FTP protocol with SSL/TLS in the Server Settings as shown in the Server Settings page, you can see my configuration on the following screenshots. I have changed some sensible data just for the screenshot to avoid problems.
I am not using the “Use relative URLs” because of the warning shown on the foot of this option, which reads: Please remember: while using relative URLs, some features like Open Graph tags, sharing buttons etc. cannot work properly.
If you think this option may solve something just let me know. Please.
Thanks in advance.
Replace public_html/blog with /public_html/blog/ and you should have no more problems. I had the same problem with one of my domains, after adding a slash at the end, it only uploaded the changed files.