This is usually a sign that Java is spending too much time Garbage Collecting. Try using -XX:+UseG1GC -XX:MaxGCPauseMillis=50 flags and increasing your -Xmx.```
https://spark.lucko.me/#AddP8yjG6x
https://spark.lucko.me/#CAwQcKYd3K
https://timings.spigotmc.org/?url=towupabege