I make almond milk regularly. One time, my whole-almond soaking period extended to 4 days instead of the usual 2 days. This batch soured and curdled sooner than the other batches.
I have also seen souring and curdling with storebought almond milk, however well-after opening and being kept inside the refrigerator.
I wonder if it's an option to pasteurize the almonds and its soaking water together in a pot, before storing in a jar? Regardless of the fact that it will later be recontaminated in my juicer and a subsequent decantation (part of my own process) -- maybe it can still lower the microbial load?
What bacteria rots the almond milk anyway?