I have had this experience, and I tell myself the viscosity of each strain will be noticeably different and even within a strain from batch to batch to a degree, so the bubbles just must have a harder time penetrating some than others. But yeah, once it goes flat after the initial purge, I will put it in the freezer, it usually takes a couple minutes at least to get it solid enough to flip this soon, and that contradicts my earlier thought of the extract being too thick for the butane to move through freely. But regardless, once I flip it and put it back in, give it 30-45 minutes to get back up to temp, then pull vacuum, it’s active as ever again, but fizzles out soon, then after repeating this for the first 36 hours or so, it starts to behave as I feel it should lol. But I 100% agree, it is a very mysterious substance, that doesn’t seem to follow exactly the same path twice, I’ve only done 10 or so runs though so, I’ve got much to learn.