vbulletin 5.5.1 install problem

[napy8gen]

Hello Guys,
I have a weird situation happened couple of times now when upgrading my demo forum.
To run the upgrade I need to change to PHP 7.1, my current PHP is 7.0
The installation went smooth with PHP 7.1 but in the front end all is broken even with default style. Attached screenshot.
But I f I change back to PHP 7.0, all is good,

Even now after upgrade, If I changed to PHP 7.1 the forum will be broken. I need to stay PHP7.0 if I want a working forum, only changed the database to 7.1 when doing upgrade.

[glennrocksvb]

Check the error logs for detailed error stack trace.

Are your CSS stored on file system or database? Try storing on file system (if not already) before the upgrade.

[Wayne Luke]

Do PHP 7.0 and PHP 7.1 have the same configuration? On many servers, they will have different php.ini files and if these aren't kept in sync, it can cause problems when you switch versions. Please make sure that you have the Minimum Requirements enabled in PHP 7.1.

[napy8gen]

Thank you Wayne. It is working now.
Glenn. When I switched to file system all the styles broken but it is not the issue now.