Melted the butter and oil together. Had placed in the fridge. Whisked it.
I'm going to take a guess here based on my last Master Batch. You didn't stir your melted oils/butter together really well and/or that not all the butters fully melted. Then you placed it in the fridge right away to harden back up so you could whip it and since the oils/butters weren't fully incorporated or fully melted, you had some separation. And now your whipped butter has overheated and the separated bits are showing up.
Usually when I Master Batch my Hard Oils/Butter, I start with the one that takes the longest to melt. In my case it's Cocoa Butter, followed by Palm Oil, then Coconut Oil, then my Shea Butter. I stir the Cocoa Butter before adding the Palm Oil, then stir that before adding the Coconut Oil. I then turn off the stove and add the Shea Butter which has been cut up into small chunks and then stir it every couple of minutes. I then give it a whiz with my Stick Blender and pour into the bucket with my Soft Oils and give it another good whiz with a commercial paint stirrer on a drill. I was in a hurry with my last Master Batch...I just dumped all my Hard Oils/Butter into the pot, dumped it into the bucket as soon as the Cocoa Butter was melted, gave it a quick stir with my long handled ladle and called it good.
I noticed the first time I went to use my MB that it was...'different', but didn't really pay too close attention. Just stuck in the paint stirrer, gave it a good mix and weighed it out. I then noticed when I was making soap, that my batter wasn't behaving like it usually does...I thought maybe that I was just soaping too warm. It wasn't until the bucket was finally light enough that I could lift it up and put it on a step-stool before stirring that I saw that I had some separation. Now depending on the temperature in the house...the consistency can range for pancake batter to cornbread batter but it is usually homogeneous. But this time it looked like I had poured in a Soft Oil into cornbread batter, but didn't get it completely stirred in. Out of curiosity, I made two small batches like I usually did and noticed that the batter thickened up quickly. The third batch, because I was doing a two-color swirl I first whizzed up my remelted oils, then gave them a quick whiz after adding my Lye Solution and separated. While the batter was still a little 'odd', I had more working time.
Sorry this is so long.
Along with making soap from my last Master Batch, I am doing wedding soaps for my son's wedding and so made two smaller Master Batches so I could keep the colors consistent with 160 soaps. I took my usual time when melting the Hard Oils/Butter and then there was extra whizzing of the oils to get the colorants well mixed in. When I made the first batch of Navy soap, it thickened up fairly quickly, but that was my fault...I was a little heavy handed with the SB. The Rust soap I was more careful with and got a perfect pour.