Sure here is the last log from moonreader where I get the same error:

Invalidated OPDS content, please contact owner of this OPDS site to verify below error:

At line 6, column 20: not well-formed (invalid token)

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:dcterms="http://purl.org/dc/terms/"
      xmlns:pse="http://vaemendis.net/opds-pse/ns" xmlns:opds="http://opds-spec.org/2010/catalog" xml:lang="en"
      xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/">
    <id>http://5c97d45ac2ab4b96abb759e355834af9-174130-folders</id>
    <title>Fantasy & SciFi</title>
    <updated>2023-12-30T07:28:49-06:00</updated>
    <icon>/collection/theme/common/favicon.ico</icon>
    <author>
        <name>Ubooquity server</name>
        <uri>/collection</uri>
    </author>

    <link type="application/atom+xml; profile=opds-catalog; kind=navigation" rel="self" href="/collection/opds/books/174130"/>
    <link type="application/atom+xml; profile=opds-catalog; kind=navigation" rel="start" href="/collection/opds"/>

    <entry>
        <title>Aaronovitch, Ben</title>
        <id>174131</id>
        <updated>2023-11-28T15:32:40-06:00</updated>
        <content type="html"/>
        <link type="application/atom+xml; profile=opds-catalog; kind=acquisition" rel="subsection"
              href="/collection/opds/books/174131/?displayFiles=true"/>
    </entry>
    <entry>
        <title>Abraham, Daniel</title>
        <id>174145</id>
        <updated>2023-11-28T15:32:41-06:00</updated>
        <content type="html"/>
        <link type="application/atom+xml; profile=opds-catalog; kind=acquisition" rel="subsection"
              href="/collection/opds/books/174145/?displayFiles=true"/>
    </entry>
...
    <entry>
        <title>Ishiguro, Kazuo</title>
        <id>176925</id>
        <updated>2023-11-28T15:35:31-06:00</updated>
        <content type="html">
        <link type="application/atom+xml; profile=opds-catalog; kind=acquisition" rel="subsection" href="/collection/opds/books/176925/?displayFiles=true">
    </content></entry>


<!-- Powered by Ubooquity -->

So I though I would delete and add my OPDS library to moonreader again incase it was caching something as I still saw the line <title>Fantasy & SciFi. However that has opened a new problem authentication fails everytime. I have a special character in my password, so removed that and tried just alphanumeric numeric and no password and they all fail with the 2 android apps I use moonreader & fbreader for OPDS feeds. If i try a browser though the opds url works everytime. I use http not https

I have been unable to find any logs inside of android that I can access for moonreader or fbreader that might show the request they are sending

here is the log with the login failures, debug mode enabled. collection is my reverse proxy

20231230 15:17:42 [Thread-1625] INFO com.ubooquity.a - Internal server started. Listening on port 2202 (library) and 2203 (admin)
20231230 15:17:58 [qtp1140697305-1717] INFO com.ubooquity.d.d - Basic authentication failed. Access Denied. [login:Expattx ][ip:192.168.50.1]
20231230 15:18:09 [qtp1140697305-1719] INFO com.ubooquity.d.d - Basic authentication failed. Access Denied. [login:expattx ][ip:192.168.50.1]
20231230 15:18:24 [qtp1140697305-1701] WARN o.e.j.server.handler.ContextHandler - Unimplemented getRequestCharacterEncoding() - use org.eclipse.jetty.servlet.ServletContextHandler
20231230 15:18:24 [qtp1140697305-1701] INFO com.ubooquity.d.d - Logon attempt with expired timestamp. Access denied. [login:Expattx ][ip:192.168.50.1]
20231230 15:18:24 [qtp1140697305-1701] INFO com.ubooquity.provider.h.b - Using template LOGIN with following parameters:
rootPath: "/collection"
loginScripts: "\n"
hiddenInputs: "
\"d0809793df2c3be1a77a229781cfe1cdb1a2a\"\
\n
\"1703971104432\"\
\n
"
formId: "loginform"
loginFieldName: "login"
passwordFieldId: "passwordfield"
onLoginClick: "submitform();"

I tried this again with version 3.0.2 and get the same error still was this included with the duplicate scan fix?

My scans show as complete now and I can launch another scan as well. On my library previously it never showed complete and after anywhere between 24-48 hrs after I started a scan the app would crash or my pc would lock up if I didn't stop the server and start again. Did you make any changes to the duplicate detection that you would like me to try out and see if there are any improvements apart from the new flag?

I had a problem with OPDS on moonreader which was caused by the & symbol in one of the category names in my library which will be fixed in the next beta version. Maybe there is a special character in your file/folder structure causing issues?

Thanks let me know if you need anymore details or anything you would like me to try

If those books are epub I would open them in Sigil and see if there is some corruption preventing them from loading properly. I use that application to change covers and descriptions for my collection. When you open a file it tells you if there are errors and where they are, and can autofix some errors.

Thanks for taking care of that.

Thank you for the explanation., I like that changes it makes it a lot easier to manage my collections.

I have have added a magazine category and now there are comics, books and magazines which all follow their folder structures. I do wonder what formats are supported by each category type, if it has changed with the reworked db calls. 

Here is a link to JDK 17, though I used 21 as that was the first link I found and it is working.

https://www.oracle.com/java/technologies/javase/jdk17-archive-downloads.html