What OP says, I've checked a dozen or so small systems around Sol that definitely had tags, and they are all gone. Its the same old bug again as when 3.3 launched.Let's just check people are not getting confused.
If a system is pre-discovered then there will be no discovered by tag.
If a system can be discovered then there will be a first discovered by tag.
If you are entering a system and scanning for the first time, you do get to "discover" it, but of course you don't get a tag. Only the first person gets that honour.
A lot of systems in the bubble are pre-discovered, so make sure you are not looking at one of those.
If indeed, non-pre-discovered systems are missing their first discovered tags, raise a bug report.