Hi,
I’m afraid this is a browser specific behaviour, the browser tries to scroll back to the original position, however the search results are not there yet, so it is miscalculated.
If you want, I can take a look at this via the source code to see if there is any way to correct. For that, please make sure to update the plugin to the latest version first (4.21.3). Then if you can add temporary FTP access I will try to debug it.