Silencing of INTEGRATED transgenic arrays?

Hi there, I have an integrated transgenic strain that displays severe locomotion defects and dumpiness. Recently these worms start to spontaneously revert back to WT both in movement and morphology. How can arrays be silenced even after they are integrated into a chromosome by irradiation? I assumed that may be transcriptional silencing of arrays have occurred because of long-term passage of the strain, but I have only been propagating this strain for 6 month. I also deforested a fresh batch 2 weeks ago and the same thing happened. It is particularly noticeable on a starved plate since all the sick and paralysed worms are clumped together, while the healthy looking ones crawl around happily. There also appears to be some in-between the two extremes. I definitely haven’t mixed up any worms since this strain has really distinctive GFP markers and they all looked green under the fluorescent microscope. Has this happened to anybody? Thank you for your help!!!