SEO bots are not reading my code properly on infinityfree hosting. Why?

Ok, so this is a weird one and I cannot figure it out. So, help me please.
Before I joined infinityfree, I was with and still have sites with 000webhost. While with webhost, the exact same webpage and code that I migrated over here was in use there. I only migrated because of their limitation of providing a free hosting plan with the ability to implement purchased SSL, which infinityfree allow.
While hosting there (exact same code), SEO bots and site analysers where ranking my website as excellent, around the 90% mark. 2 of my favourite are and nibbler.silktide with whom i rated highly on mobile optimisation and SEO.
So I migrated over here and implemented EXACTLY the same code and all of a sudden, my page is no longer optimised for mobiles (although google checker says otherwise), but my biggest and most confusing issue is this, all of my SEO code (meta, heading, title, h1-h5, etc) is all written in the website code but no bot finds it, EVER. not even google who just picks any words it sees now. My rating on the analysers plummeted to 48% and 33% with main issues being SEO.
I changed my whole code from .html to .php hoping that maybe your servers preferred code in .php format but that did not work either.
So I did a test, migrated the exact same code over to webhost again, loaded under a different domain but exactly the same site and let the bots crawl the 2 of them, The site hosted on webhost got 89%, the site hosted here got 48% again, with SEO errors and mobile issues. HOW??? They are the same code…
I am so confused, how does code work perfectly on one host’s server and works horrendously on another? The exact same coding?? Please explain if you can.

We have some security systems which prevent access from most bots. I can assure you that the crawlers of all popular search engines are not affected by this, but I don’t think most SEO checkers work so well. So I suspect the SEO checkers are not looking at your website, but at the interstitial security page.

Actually, to quote Nibbler’s own About page:

Some websites use special anti-bot technologies to stop spammers. These websites may also stop Nibbler from being able to test them.

I think that’s what’s happening here as well.

Just use Google’s own SEO checker, rather than some external tool which pretends to know exactly how Google ranks a site.

You are absolutely right.
Great answer. Thanks, make more sense now.