java.io.IOException: Server returned HTTP response code: 429 for URL: https://bStats.org/submitData/bukkit
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1997) ~[?:?]
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1589) ~[?:?]
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:224) ~[?:?]
at com.comphenix.protocol.metrics.Metrics.sendData(Metrics.java:306) ~[ProtocolLib.jar:?]
at com.comphenix.protocol.metrics.Metrics.lambda$submitData$0(Metrics.java:262) ~[ProtocolLib.jar:?]
at java.lang.Thread.run(Thread.java:833) ~[?:?]

this isn't an error with ProtocolLib, rather bstats is receiving too many requests. (this is seen where your log says Server returned HTTP response code: 429)
Please check online before posting errors. This documentation from mozilla tells you about the 429 http response code:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/429

Please close this issue.