The SimpleXLSX library doesn't work on Nginx, but it works on Apache2. What is the problem?

Question

PHP

Hello! We have a project written in PHP. In short, this project is parsing an XLSX table and displaying it to the user in the browser. For parsing, the SimpleXLSX library (version 0.7.1) is used. This project worked fine on Apache2. After transferring to the Nginx server, the library stopped parsing tables. When viewing the logs, it gives the following error:

PHP Warning: Invalid argument supplied for foreach() in /path/to/file/simplexlsx.class.php on line 314, referer: example.com

I can't figure out what the problem is. Thank you in advance!
PS: The project initially worked on Nginx, but after a server restart (adding aliases) it stopped working.
UPD: When displaying the entire initialized library through var_dump($xlsx);, it is clear that bugs are getting into the library. There is no such thing in Apache2 server. The PHP version on the two servers is the same.

Answer 1

Bitrix is ​​running on the main server. The parameter mbstring.func_overload 2 was set for it. Changed the value to 0. Everything worked.