In the GamerUserSettings.ini under the section "Server Settings" (if using expert), there is the command
This governs how much your players harvests when they hit, for example, a tree or when bashing boulders. I know that WC have increased their base rates recently, and so some experimentation is required now. The new base rate is x2.0, so if you had your rates at x3 the WC original default, I guess you'd need to put the value at x1.5 to keep it as you had before. I must admit that I am not entirely convinced that the new WC base defaults have carried over to private servers. I used to use the number of individual stones you picked up from the floor as an indicator as to what your harvest level is at. Apparently that is not reliable anymore as the stone picks ups have been set to one, or so one of the mods seemed to suggest the other day. However, if I set my harvest rate at x2.0, I do in fact pick up two stones. I am a little confused.
There is also another multiplier
This is described on the settings wiki as: "optimized" server with high HarvestAmountMultiplier (but less rare items).
Might be worth checking if you have that set to true (it's also under Server Settings in the GameUserSettings.ini