While you type in command /function #minecraft:tick, it just doens't work. What's more, the server side doesn't seem to load the source. But the weird thing is that the #minecraft:load function tag still works.

Actually I tried to look into the codes, but I'm still new to Java and don't know what's the problem. The only thing I can say is that the bug's probably at 
net.minecraft.server.ServerFunctionManager
 

EDIT: Well it turned out that I made some mistakes in the code, not Minecraft's fault OWO

Sorry for the bad English >/////<