I should preface this by saying that this is not an "Is my beer ruined?" thread, and I don't need to RDWHAHB.
I pitched my second batch of cider yesterday and have witnessed the same result with each. Fermentation has kicked off quickly (using an ale yeast) and within 8-10 hours, I have a healthy layer of krausen on top, about 2 inches thick. Within the next 6ish hours, however, the krausen has fallen and is completely gone, though the yeasties continue chewing away for the next few days, still bubbling like crazy. The first batch fermented out completely in reasonable time and tastes great, so everything seems to be healthy.
I'm just curious if it's standard for krausen not to stick around with ciders or what? Maybe fewer proteins etc. to contribute to head retention means not as much foam during fermentation?