What is going on based on bubble size?

I have some cider that I racked off into secondaries. After a couple days it started to wake up again and after 2 weeks the bubbles changed from a slow but steady flow of larger bubbles to a fast flow of microbubbles all while only slightly changing the volume of Co2 coming out of the airlocks.

Is the size of bubbles a change in what is fermenting? Is this part of the malic acid changing into lactic acid? Is this something dreadful happening?

Mine did the same thing this year. Plus a lot more lees in the secondary.

If it is cider from apples that wasn't pasteurized, overly sulfited, and it is warmer than 70 degrees, it ought to be MLF taking place. This can go on for three months. Traditionally all aged fermented cider would have experienced Malolactic fermentation.

It's only 62 deg. F now. A month ago it was 68 deg. F.