I’m frustrated

C# Business rule not working on some computers

I have a project that I have recently updated to include a C# custom business rule.
However, 2 of my customers PCs are not running the business rule. When I test on my side the rule works perfectly. What could be the problem?
I am using COT and my project is running on classic UI.

The problem has been going for a while now and i do not know how to solve it...
It is extremely frustrating since I do not have access to the customers computers
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