Missing blocks

I built a kelp farm on 06/30/2020, consisting of 16 pistons lined up in one row. 16 observers were placed on top of all pistons. The farm was functioning properly until I logged in today, 07/06/2020. I noticed that 11 of the 16 pistons were now missing. I have attached 2 photos showing the missing pistons and a photo from 06/30/2020 showing the pistons correctly in place.