Throughout my time playing on my server, I have experienced performance issues when:

• There are more than 3 or 4 people on the server at a time.(tps goes down)
• Running a redstone machine (tps goes down)
• Using Haste 2 (block lag and ghost blocks)

The decrease in performance has also made taking off with elytra almost impossible and unpredictable, going through portals to other dimensions takes longer, eating takes multiple attempts to work. 

to troubleshoot, i have lowered the render distance and simulation distance on the server settings with no increase in performance whatsoever. I can also see that while experiencing these issues there is no increase in ram or cpu usage whatsoever, it stays below 20% ram usage and below 10% cpu usage. All the other members of the server have also experienced these issues.