The title says it all. The attached profile results are from idling in our main nether hub, where there is a powerful elytra launcher (a couple of hundred boats) nearby [1].

This did not use to be a problem, but since 1.13, as the attached profile results indicate, the server runs at 3 TPS and is no longer playable.

Also, since there are two fairly weak launchers in the spawn chunks, the maximum attainable TPS are currently about 5-6 when idling at spawn.

In case it helps, we're a snapshot server and ran into lag issues a while back, when trying to upgrade to 17w46a. We subsequently ran 17w45b up to this point, trying the newest snapshot once or twice in between to see if it was playable. It's my strong impression that the issue is the same.

[1] Before someone doubts me, yes, I managed to build an elytra launcher in the Nether. It involved stacking them in the Overworld, teleporting them to the nether, and then pushing them through a hole in the bedrock ceiling with pistons while being VERY careful not to disturb them.