When using some German or Italian systems the service names can contain some special language chars. The plugin is working fine because the value receiving from SNMP is UTF-8 decoded (when you don't use --source-encoding UTF-8 is the standard).
The problem is when use a filter to filter only one specific service the filter will not be decoded. So the plugin will filter with a regex that not matches because the filter is not decoded.
The check fails
decode the filter, too and the check will work fine
and the check works