This is what the messages.log shows.

*** Recovery started at Sun Mar 10 19:29:16 2024
     Current default directory: e:\intersystems\iris\mgr
     Log file directory: .\
     WIJ file spec: e:\intersystems\iris\mgr\IRIS.WIJ
Recovering local (e:\intersystems\iris\mgr\IRIS.WIJ) image journal file...
Starting WIJ recovery for 'e:\intersystems\iris\mgr\IRIS.WIJ'.
WIJ file not found.
Exiting with status 3 (Success)
03/10/24-19:29:16:564 (5648) 0 Automatically configuring buffers
03/10/24-19:29:16:579 (5648) 0 Allocated 1224MB shared memory: 1024MB global buffers, 35MB routine buffers
03/10/24-19:29:16:579 (5648) 0 Intel Sandy Bridge AES-NI instructions detected.
03/10/24-19:29:16:657 (5648) 0 Creating a new WIJ file
03/10/24-19:29:16:772 (5648) 0 New WIJ file created
03/10/24-19:29:16:830 (5648) 0 
Startup of InterSystems IRIS [IRIS for Windows (x86-64) 2018.1.2 (Build 609U) Thu Aug 23 2018 10:30:25 EDT]
    in e:\intersystems\iris\bin\
    with mgr: e:\intersystems\iris\mgr
    with wij: e:\intersystems\iris\mgr\IRIS.WIJ
    from: e:\intersystems\iris\mgr\
  OS=[NT], version=[6.2.9200], 2 processors.
  Processor type=[8664], level=[6], revision=[20225], active processor mask=[3].
  System Initialized.
03/10/24-19:29:16:908 (6032) 0 Write daemon started.

Any idea?

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?