Mould on my medicated butter

I was looking forward to making some cookies today and opened up the container where I keep my homemade medicated butter only to find...mould...black and white mould....on the surface and edges. I assume I'll have to throw it out rather than simply scrape off the mould and go ahead with my baking project? That said, I've been doing this for years and have never seen this before. What happened? I've literally kept med-butter in my fridge for weeks if not months before and never faced this. I always use the same process - grind up flower and trim, cook in melted butter and water so the butter doesn't burn, strain through cheesecloth.

Wasnt sealed properly or it got contaminated? Do you usually use that tupperware?
I'd use glass jar/ sealing lid, next time.

Yes, I usually use that container....though I just remembered that this time around I threw a couple tablespoons worth of "Vegan Block" into the dairy butter...maybe that's the culprit or, like you say, not properly sealed. Anyway, I just threw it out and wanted to vent a little bit! A lot of time and labour wasted, but better safe than sorry. It's strong butter and I wouldn't want to be highly medicated and simultaneously worrying about getting sick!

I would use glass bottle too. Some type mason jar with sealing lid. I would never use plastic although I’m no expert.