@Hypolite Petovan

After a break I started to check out everything again and did several tests.
I changed the order of the lines in local.config.php and managed to get the exact same lines and order in the bin/console prints of both sites.
The problem stayed.
Than I checked example_local.config.php to compare and found that actually any of the lines figure there, so I deleted them all together.
Right now local.config.php looks like this:

        'config' => [
                'admin_email' => 'anyname@subdomain.com',
                'sitename' => 'sitename',
                'register_policy' => \Friendica\Module\Register::CLOSED,
                'register_text' => '',
        ],

        'system' => [
                'ssl_policy' => 1,
                'default_timezone' => 'UTC',
                'language' => 'es',
        ],

The site still behaves the same way. At first it loads correctly, and quite fast, after some minutes it starts taking lot's of time and ends up like in the screen of the initial post.

Now the bin/console config print shows only the following two specific lines related to the whole path issue, all the other references mentioned above are gone.
I have no idea how to delete the remaining references. Those lines have to figure somewhere in the DB I guess, but again, no idea what lines to execute to display them or delete them:
config.system.basepath => /
system.basepath => /var/www/subdomain

@Hypolite Petovan

What do you mean by "works for a few minutes"? How many pages correctly show in the mean time? What happens when the few minutes have elapsed?

The site works correctly for several minutes.
I can log in.
All pages show correctly, including admin pages.
Once it falls back to redirecting to:
sub.domain.com/var/www/subdomain/
.. I have to execute again:
/var/www/subdomaincom/bin/console config system url https://sub.domain.com
.. the console prints (as always):
system.url <= https://sub.domain.com
and I can use the site again for several minutes before it falls back to the wrong behavior.

@utopiArte Once you set a config value using the console, changing the value in the config file won't help as the console stores the value in the DB and it has precedence over the files.

No matter how you did it, the important part is that system.basepath must be set to the install folder, and system.url must be set to the full URL. You can verify what the current value used by Friendica for either config keys is using the console.

I've browsed https://inversion.tupambae.com and when the style is missing, the first line shows inversion.tupambae.com/var/www/inversioncom even though it should show https://inversion.tupambae.com. This is governed by the system.url config key.

@Hypolite Petovan

To me it "feels" that /var/www/subdomaincom is added by some mecanism to sub.domain.com. In particular because when setting specifically with the console command /var/www/subdomaincom/bin/console config system url -> https://sub.domain.com it works for some minutes.

@Hypolite Petovan

As last intent I tried to use the following commands to reset the two mentioned settings but the behaviour ist still the same:
/var/www/subdomaincom/bin/console config system url https://sub.domaincom
/var/www/subdomaincom/bin/console config system basepath /var/www/subdomaincom/

Can't see a solution for this.

@Hypolite Petovan

No I can't.
There is no change at all in the results of the bin/console config output (print).
Actually even the settings send and "officially" accepted by the system do not show up in the print.

Latest thing I tried, totally feed up, was to send the commands several times and also making sure they end with a slash.

So I send:
/var/www/subdomaincom/bin/console config system url https://sub.domain.com/
system.url <= sub.domain.com/
/var/www/subdomaincom/bin/console config system basepath /var/www/subdomaincom/
system.basepath <= /var/www/subdomaincom/
/var/www/subdomaincom/bin/console config system url https://sub.domain.com/
system.url <= sub.domain.com/
/var/www/subdomaincom/bin/console config system basepath /var/www/subdomaincom/
system.basepath <= /var/www/subdomaincom/

And right now it looks like it sticked, for now the site remains operative!
🙄

(please have in mind that this is 2021.04, if it weren't so outdated I'd say we need to figure out the problem because this feels like a real problem under the hood)

@Hypolite Petovan

Well now strangely on both sites bin/console config doesn't work anymore.
Both throw the following error message:

rootName@VPShosting:# /../doamincom/bin/console config
PHP Fatal error: Uncaught Error: Undefined constant "CURLE_OPERATION_TIMEOUTED" in /../domaincom/boot.php:229
Stack trace:
#0 /../doamincom//vendor/composer/autoload_real.php(69): require()
#1 /../doamincom//vendor/composer/autoload_real.php(59): composerRequireFriendica()
#2 /../doamincom/vendor/autoload.php(7): ComposerAutoloaderInitFriendica::getLoader()
#3 /../doamincom/bin/console.php(31): require('...')
#4 {main}
thrown in /../doamincom/boot.php on line 229

Can't recall doing anything at all, accept trying to get the php imap module to work.