Blank page after installing on third level domain

[Manaus]

Hello, 
I tried to install PW on a subdomain. Installation was perfect, all requirements met, all lights green. After installation I got a blank page. No errors whatsoever. I tried to change the php version up and down, no change. I read somewhere here in this forum that htaccess might be to blame, but I did not change the one PW put on my server. I checked also the server log, asked support about it (client denied by server configuration). They say it's up to the User, server is ok. On frontend I got a Fatal Error: Uncaught Error: Class 'Pages' not found in wire/core/ProcessWire.php:575. Removed install.php and install folder. Nothing. Debug in config file is set to true, php version is 7.4 for PW 3.x. Database tables were created. 

One note, the domain is a third level domain, so abc.mydomain.com etc. 

Installed PW many times, this time I'm not getting meaningful data from the app. 
Thank you very much for any hint. 

[BrendonKoz]

ProcessWire can sometimes "steal" the reported errors from the webserver log. Did you check in the logs folder under "site/assets/logs/*"? There are errors.txt and exceptions.txt, and http404.txt. Maybe even file-compile.txt?

If htaccess is not correctly rendering, the error logging might never be reached, but it should be quick to check this.

Did you check the various htaccess files for any settings related to subdomains? Your site/config.php file sets the subdomain as the httpHost?

[monollonom]

2 hours ago, Manaus said:

Removed install.php and install folder.

Do you mean you removed these manually? If so then the installation must have failed as these are supposed to be deleted automatically once the admin account is created.

[Manaus]

This is the error I get, just after the installation routine (DB connection, Profile import, cleanup)

Fatal Error: 	Uncaught Error: Class 'ProcessWire\Pages' not found in /home/mysite/domains/domain.mysite.it/public_html/wire/core/ProcessWire.php:526 Stack trace: #0 /home/mysite/domains/domain.mysite.it/public_html/wire/core/ProcessWire.php(302): ProcessWire\ProcessWire->load(Object(ProcessWire\Config)) #1 /home/mysite/domains/domain.mysite.it/public_html/index.php(52): ProcessWire\ProcessWire->__construct(Object(ProcessWire\Config)) #2 /home/mysite/domains/domain.mysite.it/public_html/install.php(119): require('/home/mysite/...') #3 /home/mysite/domains/domain.mysite.it/public_html/install.php(1809): ProcessWire\Installer->execute() #4 {main}   thrown (line 526 of /home/mysite/domains/domain.mysite.it/public_html/wire/core/ProcessWire.php)

The only error I get from the logs. 

Attached is same but with colors

Thank you very much