Why malware persist to appear on Intune even device already did full scan and no threat found?

Dear all,

 On Intune we can go to Antivirus - active malware that we know which device have been detected malware and we will take action to full scan then remove malware. Here's question is we have some device already ran full scan and no threat found but there's always persist malware detected from devices. I ask MS support from Intune portal, they said I should ask for Windows client management support for help and remind me that I can post this issue on community to see if I can get reason.