The certificate is valid, its original format is PFX and I can use it in other applications.
Perhaps its conversion to .PEM to configure in IRIS is causing the problem.

However, the first certificate was also PFX and was converted to PEM, it worked perfectly. I used OpenSSL to convert both in the same way. But I don't know if in this specific case I should take any different action.

Robert, thanks for the answer, it guided me to find the causer.

I identified in the application log that it is giving an Illegal web request error, from a SOAP class that exists in the namespace.
Probably someone is insistently calling this class externally in the wrong way, and IRIS is storing errors on every call. Is there a way for me to parameterize the namespace so that it doesn't store this error?