Server tps problem

ive some problems with tps (timings:
core: 1.12.2 paper
machine: 8gb ram, r9-3900x (2 cores)
About problem: ive big tps drop, online 6-7 players and tps drops to 18,6 (in timings record was 18,73), then server starts freeze and ping jumps to 300-400
about server: all world are loaded by worldborder (5k blocks), view-distance is 4, all cores configs are optimized, ive plugins such as clearlagg

The most interest thing is - cpu and ram usage isnt so much. Cpu usage 15-20% and ram usage 4-5gb

You are using unsupported software, and aren’t even using the proper startup flags.