This is a description of my experience configuring the mod, which I tried after 6.6.2 update.
The problem occurred when I updated the mod on my server - cows stopped dropping beef.

In wiki for drop item configuration we see two settings for drops:

cowDropRawBeef: A boolean value that determines whether cows should drop raw beef.
witherDropNetherStar A boolean value that determines whether the wither should drop a nether star.

Which can be interpreted as:

Will cow drop beef? - true/false
Will wither drop nether star? - true/false

This is completely fine.

However, in config file comments and in source code they mean completely opposite things:
The cow loot drop behavior:

    public final ForgeConfigSpec.BooleanValue disableCowDropRawBeef;

The wither loot drop behavior:

    public final ForgeConfigSpec.BooleanValue forceWitherDropNetherStar;

Config file comments:

• For cow

	["Additional Drop Settings"."Cow Drop Settings"]
		#Disable cow raw beef drops.
		cowDropRawBeef = false

• For wither

	["Additional Drop Settings"."Wither Drop Settings"]
		#Enable/Disable forced nether star drops from wither.
		witherDropNetherStar = false

To summarize:
It was not obvious from config file comments and wiki combined, that I have to disable cow drops and enable the wither drops considering the variable names are built identical.

Nevermind, it was updated yesterday. :D