The Github branch source plugin seems to interact with the Global Pipeline Libraries configuration. I have a library configured there and set up the "Discover Branches" and "Discovery Tags" behavior (see screenshot).

I have created a set of tags on the repository included here:

1.0
1_0
release-1.0
release-1_0
release_1_0
taggy

Of those, the following get discovered:

1.0
1_0
release_1_0
release-1_0
taggy

The following tags are not discovered:

release-1.0
release_1.0

I can make no sense of this. It is 100% reproducible but I see no logic on why these two tags are not discovered by the plugin.

This is a GHE setup using a local GHE server.