I see from FACT-1405 that you've fixed this particular issue for nexthop flags, but not for all flags. I cam across the following errors for the notify flag. Could this fix be expanded to handle all flags in the routing table?
puppet-agent[32368]: (Facter) Could not process routing table entry: Expected a destination followed by key/value pairs, got 'default via XXX.XXX.XXX.XXX dev eno1 proto unspec notify'
puppet-agent[32368]: (Facter) Could not process routing table entry: Expected a destination followed by key/value pairs, got 'XXX.XXX.XXX.XXX/24 dev eno1 proto unspec scope link metric 100 notify'
The right way to fix this is probably just to give up trying to parse key/value pairs and scan for the keys we want. We've had at least one or two similar tickets, and special-casing them all isn't worth it anymore.