Rows moving to the bottom of a sheet on its own



I've been noticing this for about 6 months now, every now and then on one of my sheets, at least 20 rows that were close to the top of the sheet randomly move to the bottom of the sheet. Haven't lost any data (thankfully) when this happens and I have to drag it back to the top.

Is this a glitch and how can I stop this from happening?