The .jcheck/conf file was updated in JDK-8252844 to the new Skara format. There seems to be a mistake in the regex for valid tags, since most formerly valid tags are now listed as invalid.

$ git jcheck
[tags] error: illegal tag name: jdk-10+0
[tags] error: illegal tag name: jdk-10+1
...
[tags] error: illegal tag name: jdk9-b93
[tags] error: illegal tag name: jdk9-b94