Unspecified field in commandFunctions debug dump

My server is constantly reporting "Can't keep up!" with a tick delay of around 2000ms.

Spec-wise, the server is not slow. I gave the Minecraft Vanilla Server 1.13.2 enough RAM and no further Java flags besides of "-server". 

It has a bunch of datapacks installed, but most of the resource is drawn from the unspecified field under commandFuntions shown in the debug dump. What does it represent?