If you are absolutely positive your server is clean (If it was me and it was possible, I would be ditching it completely and setting up a fresh hosting account and telling the host the previous site got compromised). If you have restored the site from a backup from the server, it is also possible that you have reinstated any nasties that were lurking.
Im assuming you have changed all passwords for SFTP and SSH etc? If your using plain FTP, disable it, it’s not secure.
You could try renaming the panel. Theres a guide here.
On a side note, the sites footer still says 2018. Kirby text can help here (will update itself):
I’d get in contact with the hosting support and discuss this issue with them. Most or all hacked sites we had in the past were related to using weak FTP instead of SFTP.