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Apparently, 1.7.x doesn't work with PacketEvents, I recommend use legacy versions for the moment. Probably some checks go to work with Bukkit Events if packetevents isn't in the server, like legacy versions (but with ProtocolLib).
Reset your checks.yml and language.yml if you want this changes, if you don't reset, this still go works correctly with your actual config (if is 1.2.1).
Report any error or give your suggestion in the discord server support.

FoxAddition is an anti-cheat plugin designed to block certain types of hacks, possible to use it with another anti-cheat plugin making it an additional anti-cheat for your server.