Web page appearance glitching

Site URL: https://www.hornhavenmusic.com/

Hi there,

I visited my webpage and was dismayed to find problems with the layout.  In the example I attached, you can see a lot of overlap and crowding of text blocks etc near the top of the page. The other attachment is of the page loaded properly.

Refreshing the page fixed the problems only rarely.  Most of the time, the page loaded in various bizarre ways.

I tried closing and reopening the browser (Firefox) and also opened with Internet Explorer with similar inconsistent results.

The appearance of the pages while editing in Squarespace are what I would want.

Any help with this appreciated. I'd like to safeguard my pages against random results for visitors.

Thanks in advance,

David