I tried to find other way how to fill kettle with milk but... the only way is to milk a cow... I have only modded cows on my farm and can't milk the with kettle (and I don't want to see standart MC cows on my farm). So... Can you add a recipe like this: kettle + milk bucket = milk kettle + empty bucket. I think this could be useful... Thanks for your attantion. (I will add a pull request with this addition if I get enougt time to do it)

Sorry. For some reason I have a bug and can't fill kettle with milk even with milk bucket in my hands. I will try to find the reason... I think some mod conflicts...

hmm, that sounds like a mod is either overriding the milk bucket or its right click behavior.

can you ensure if the ID shown for your milk bucket when using advanced tooltips (F3+H) is indeed minecraft:milk_bucket?

also, if you can send me your latest.log file (in .minecraft/logs/latest.log) I can see if there's any errors being thrown. thanks!