When validate url this message show:
"URL validation failed to due to the absence of the expected JSON-containing AMP_VALIDATION comment after the body."

Expected Behaviour

Show the errors of validation

• WordPress version: 5.3
• Plugin version: 1.4.1
• Gutenberg plugin version (if applicable):
• AMP plugin template mode: transitional
• PHP version: 7.3
• OS: Centos 7
• Browser: [e.g. chrome, safari] Firefox
• Device: [e.g. iPhone6]

In the log files I have messages related to the use of is_amp_function related to a plugin, but when this plugin is disabled, the messages go away and the issue with validat url continue.

In the acces log file I get this:
/wp-admin/edit.php?post_type=amp_validated_url&amp_validate_error=response_comment_absent&amp_urls_tested=0

I have tried adding ?amp&amp_validate (as stated in #1733) to the url, get the same mesage when a try to view the validation errors.

iconv is installed as estated in #3207

With all plugins disabled and a default theme, the issue is here.
I have a list of plugins that when enabled the amp validator icon in admin side have issue, but cannot view cause this:

Autoptimize
jQuery Updater
Sassy Social Share
Lazy Loader

But urls get amp validated in google and in amp validator.

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