I use Google Search Console to see how the crawler sees my page with a "Fetch & Render" option.
In the results:
- Fetching tab: I can see the whole valid HTML without any errors
- Rendering tab: The top of the page renders fine, but it stops rendering at some deep scroll point
The page has 3,260 words 18,458 characters of the main content.
I validated it with v3 HTML validator and its OK, except some irrelevant errors from Yoast Breadcrumbs which do not collide with other pages.
I did check it on 7 devices so far and on four main browsers (Firefox, Chrome, Opera, Edge) and it does fully render.
If I see the whole HTML fetched, should I be worried about the full HTML not rendered in the Search Console?