Failed to get SAVI instance

This Morning I got calls from my Users that Accessing the Internet is no longer possible. Error they get for EVERY Site: "Failed to get SAVI instance"

So according to other Articles I found I switched a) from Dual-AV-Scan to Single-AV-Scan in my Web-Protection Filter-Actions AND b) from Sophos to Avira as my Single Scan Engine in "Management-System Seetings-Scan-Settings". After that, accessing the internat was possible again for my Users.

[9.006-5] SAVI engine scan failed - Web Protection: Web Filtering & Application Visibility/Control - UTM Firewall - Sophos Community

UTM - Virenscan Fehler (Webfilter / E-Mail-Security) - German Forum - UTM Firewall - Sophos Community

Before that I tried to turn off an on "Web Filtering Status" via GUI, but that does not correct the error.

What I will do next ist to restart the whole UTM, but that will be possible this evening/tonight and not now.

Mails seem to come in normally, even if "Dual AV Scan" ist still activated under "E-Mail Protection-SMTP-Malware", what seems strange to me.
Why does Dual-AV-Scan harm Web- but does not harm Mail-Protection, assuming that ist is the same Sophos-Engine with the same Patterns?

Does anbody else - today or in the past - had this error and can share what helped?

Thank you!!