Hi @eze008
Thank you very much for your reply!
I ran the websites through Malware checks and no problems were found. I checked through Google’s Transparency Report: https://transparencyreport.google.com/safe-browsing/search and through Unmask Parasites: https://www.unmaskparasites.com. There doesn’t seem to be any strange files uploaded recently as well via FTP, only the ones I worked on.
Do you perchance have any other ideas on what can be done?