lemminx: Unable to work with modular DTD?

Problem

When editing a file with correct DOCTYPE and available DTD files I get message saying the DTD has 41 errors:

The DTD in question is the JATS (Journal Article Tagging Suite), which is a NISO Z39.96-2019 standard maintained by the NLM (U.S. National Library of Medicine), and it most certainly does not have any errors.

I feel that the server is working, for when I remove the system identifier I get the correct error:

Please, any ideas as to what might be wrong?

DTD library and test file

This DTD is available at ftp://ftp.ncbi.nih.gov/pub/jats/publishing/1.1d3/JATS-Publishing-1-1d3-MathML2-DTD.zip and is composed of the following files, which include a sample test XML file (marked below).

./
├── catalog-jats-v1-1d3-no-base.xml
├── catalog-jats-v1-1d3-with-base.xml
├── iso8879
│   ├── isobox.ent
│   ├── isocyr1.ent
│   ├── isocyr2.ent
│   ├── isodia.ent
│   ├── isolat1.ent
│   ├── isolat2.ent
│   ├── isonum.ent
│   └── isopub.ent
├── iso9573-13
│   ├── isoamsa.ent
│   ├── isoamsb.ent
│   ├── isoamsc.ent
│   ├── isoamsn.ent
│   ├── isoamso.ent
│   ├── isoamsr.ent
│   ├── isogrk3.ent
│   ├── isomfrk.ent
│   ├── isomopf.ent
│   ├── isomscr.ent
│   └── isotech.ent
├── JATS-ali-namespace1.ent
├── JATS-articlemeta1.ent
├── JATS-backmatter1.ent
├── JATS-chars1.ent
├── JATS-common1.ent
├── JATS-common-atts1.ent
├── JATS-default-classes1.ent
├── JATS-default-mixes1.ent
├── JATS-display1.ent
├── JATS-format1.ent
├── JATS-funding1.ent
├── JATS-journalmeta1.ent
├── JATS-journalpubcustom-classes1.ent
├── JATS-journalpubcustom-mixes1.ent
├── JATS-journalpubcustom-models1.ent
├── JATS-journalpubcustom-modules1.ent
├── JATS-journalpublishing1.dtd
├── JATS-link1.ent
├── JATS-list1.ent
├── JATS-math1.ent
├── JATS-mathml3-mathmlsetup1.ent
├── JATS-mathml3-modules1.ent
├── JATS-mathmlsetup1.ent
├── JATS-modules1.ent
├── JATS-nlmcitation1.ent
├── JATS-notat1.ent
├── JATS-oasis-namespace1a.ent
├── JATS-oasis-namespace1.ent
├── JATS-oasis-tablesetup1.ent
├── JATS-para1.ent
├── JATS-phrase1.ent
├── JATS-references1.ent
├── JATS-related-object1.ent
├── JATS-section1.ent
├── JATS-XHTMLtablesetup1.ent
├── JATS-xmlspecchars1.ent
├── mathml
│   ├── mmlalias.ent
│   └── mmlextra.ent
├── mathml2.dtd
├── mathml2-qname-1.mod
├── mathml3.dtd
├── mathml3-qname1.mod
├── oasis-exchange.ent
├── Smallsamples
│   ├── journal.elementa.000011.xml
│   ├── journal.elementa.000012.xml
│   ├── journal.elementa.000017.xml
│   └── samplesmall-pub1.xml                                          # this is the test file
├── xhtml-inlstyle-1.mod
├── xhtml-table-1.mod
└── xmlchars
    ├── isogrk1.ent
    ├── isogrk2.ent
    └── isogrk4.ent