I'm on a modded 1.12.2 Forge server and I play with my friend (only 2 people are ever online at once). We have 10 chunk render distance. We have 25 mods installed, and the server runs fine. Even with DaVinci's Vessels, the server can handle ships of 1-2 thousand blocks. The issue comes with ships more than 2500 blocks in size. We recently built a flying submarine that has 3,100 blocks (most of which are air balloons). When we try to assemble the ship, it lags and turns it into an entity (so it's fine assembling it). When I try to move it, it will move, but then rubberband back into its previous position. It repeats this for a minute or two and then times both of us out. When I join back everything is fine. Please not that during this time the server doesn't have abnormally high ram usage. This is very frustrating, and I know it's a lot to ask, I just want to know if there's any way that I can make this better and usable. We spent a lot of time on this project and I want to be able to use it, and it seems that the server isn't working that hard. Is there a way to see cpu usage for the server? Is that the issue? My internet is 500 mbps download with 20 mbps upload (and they rarely go above 10 megabits used for each, so my internet is fine). Please tell me there is a way to solve this, because I want to fly my submarine! Either way, thanks for any help anyone can give. I can also add screenshots or videos if anyone needs them (I don't know if I'm supposed to add them so I'm not putting any attachments for now).
Edit: for some reason when I tried to use the account that owns the server for the forums, it said the name didn't exist, so I just made this account so I could make this post. I do have access to everything regarding the server though, it's just on a different account.