The joinlemmy crawler is throwing an error on hexbear.net. Problem is that /api/v3/site is returning an unexpected value for version which fails to be parsed. You can run the crawler yourself to reproduce:

cargo run -- --start-instances hexbear.net --verbose 5
Finished dev [unoptimized] target(s) in 0.28s
Running `target/debug/lemmy-stats-crawler --start-instances hexbear.net --verbose 5`
Crawling...
DEBUG - Worker 0 starting job hexbear.net at distance 0
TRACE - Job hexbear.net errored with: unexpected character '.' after patch version number
Crawl complete, took 1s
Number of Lemmy instances: 0
Total users: 0
Half year active users: 0
Monthly active users: 0
Weekly active users: 0
Daily active users: 0

Use --json flag to get machine readable output

So it currently only supports versions like 1.2.3. You can either change the version number or change the crawler code to make it work.