I'm trying to access the scanner functionality of some Ricoh All-in-One printers from a workstation with Debian Stretch using Vuescan, but none of the means I've used can find any of them: neither scanimage nor sane-find-scanner detect them even with the net backend enable from conf files; simple-scan, xsane and VueScan either show an error message telling me there are no scanners available or lock and the avahi-daemon can't detect any _scanner._tcp or _uscan._tcp services. However the printing function works without any issue in all of them.
I used Wireshark to try and findout what is happening, and for VueScan the mDNS queries with the questions about available services aren't fully answered (it asks for both printer and scanner services, but the mDNS responses only show answers for printer services).
I can tell its not an issue with the scanners themselves as they work normally when operated manually and I don't think its a firewall issue as I have both wiped clean its connection rules and added rules that should allow communication from and to the machines from any port and the end result was the same (no scanning from PC). I even tried connecting my workstation with one of them directly, but still nothing.
I've talked with VueScan's customer service but the last thing they could think of was a problem or changes in the machines' front panel or firmware.
How can I get Vuescan to find and use the scanners?