Foam disappearing and rebuilding repeatedly on a sugar/ date wash.

[Marin7]

Has anyone observed a ferment that's going strong and suddenly loose almost ALL bubbles/ foam from surface, only to rebuild again within minutes and keep repeating this cycle?
I have 3 one gallon jugs going side by side with a sugar and date . wash. Each slightly different. One has added molasses, other has mashed banana added and last straight sugar and dates. All adjusted to a 1.075 SG. pH 5.6. The two ferments with additions, seem to be fermenting normally with a constant layer of bubbles/ foam on the surface the whole time. The last gallon is straight sugar and date wash, that (seems) to be fermenting normally.
There is consistent bubble output on ALL 3 airlocks, but in this last gallon, the bubble/foam disappears/breaks in 3-5 seconds and then rebuilds back to normal within 3 minutes.
Roughly every 10 minutes all the foam breaks and then rebuilds in a cyclic manner. It has been doing this for 4 days. First time I noticed the surface clear of bubbles, I assumed the ferment had stopped but when I looked at the airlock, it was still bubbling like normal. Minutes later the foam was back. Later the same day, I again noticed no foam on surface of that gallon jug so started watching it and realised it kept doing this repeatedly. So I started timing the intervals. They are not exactly consistant intervals, but the cycle repeats every 5 - 10 minutes max. Bubble/foam disappears rapidly n 3 to 5 seconds, then within 30 seconds starts to rebuild. Within 3 minutes the foam is back and same thickness as before.

Anyone ever see anything like this? Any explanations?