Upgrade to v2.1 -> Printer don't show any SNMP informetion

I can recommend the following steps again.

cmk --debug -vvII hostname

Inside this output the content of OID .1.3.6.1.2.1.1.1.0 and .1.3.6.1.2.1.1.2.0 are important.
If both values are empty you need to configure the rule “Hosts without system description OID” for this host. If this is done you should use the “Disabled or enabled sections(SNMP)” rule to explizit activate the relevant SNMP sections for this device.

For printers i would use the sections

printer_pages
printer_input
printer_output
printer_alerts
printer_supply

If you do then a “cmk --debug -vvII hostname” you should see inside the line

   SNMP scan found .....

The found sections and your configured sections.
If there are no printer section then there is a real bug in the handling of explizit enabled sections for v3 devices.