Render Jumpy / table glitchy.

My first datatable. Works ok, but....

I have a datatable populated by a php generated html table so the data is in the DOM for SEO. It builds out the table then jumps down to size, so there is quick noticeable glitch. 400 rows.

Is there a best practice for a smoother render?
I am not strong on front end.

thanks for any ideas.