Symfony version(s) affected

4.3, 6.3, 6.4

Description

I upgraded a SF 4.3 project to SF 6.3 (and now 6.4) - since the beginning (4.3) web profiler toolbar wasn't showing off on my browser (tried different browsers), unless loading a different template from base.html.twig.
At first I thought it was a firewall issue, but then I found out it actually pops out if I delete all render calls on base.html.twig:

<div class="container">
	{{ render(controller(
		'App\\Controller\\Website\\Base\\CompanyProfileController::getHeaderInfo'
		)) }}
	{{ render(controller(
		'App\\Controller\\Website\\Base\\WebsiteController::getUserMenu'
		)) }}
	{{ render(controller(
		'App\\Controller\\Website\\Base\\WebsiteController::getLanguageDropdownMenu'
		)) }}
</div>

to

<div class="container">
</div>

... along with a few more.
Deleting those calls, it will always show web profiler toolbar.
Without deleting them, it will show toolbar 1/10 times, 9/10 resulting in an error.

The only error "message" network tab is showing is: Failed to load resource data with target url https://127.0.0.1:8000/_wdt/d73375 .
If I open https://127.0.0.1:8000/_wdt/d73375 on a different tab, it will load it.
It may seem a php memory limit issue, so I set memory limit to 2048M, and then to -1 (no limit), without success.

I just noticed what could actually cause this weird behavior.
When it's not rendering, Symfony logs show this error:
httputil: ReverseProxy read error during body copy: fcgi: invalid header version

However I don't really know what to do with that.

How to reproduce

Try running a really heavy project (with a lot of SQL calls). Run symfony server:start and see if web profiler shows.
Just to give you an idea, here's the profiler data one of the few times it rendered.

Possible Solution

I just noticed what could actually cause this weird behavior.
When it's not rendering, Symfony logs show this error:
httputil: ReverseProxy read error during body copy: fcgi: invalid header version

On the other hand, when the profiler toolbar successfully renders, this error doesn't show at all.

Additional Context

No response