log4net seems to lack permission on IIS - asp.net

Question

Context :
Windows 2019 Server
ASP.NET MVC using .NET Framework 4.5.2
log4net 2.0.12
In web.config (inside <configSections>) I have:
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
In the same file (inside <configuration>)
<log4net debug="true">
<root>
<level value="ALL" />
</root>
<logger name="inboundAPI">
<level value="ALL" />
<appender-ref ref="RollingFileAppender" />
</logger>
<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
<file value="C:\temp\inboundAPI.log" />
<appendToFile value="true" />
<preserveLogFileNameExtension value="true"/>
<rollingStyle value="Date"/>
<datePattern value=".yyyyMMdd"/>
<staticLogFileName value="true" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level - %message%newline" />
</layout>
</appender>
</log4net>
Finally inside Global.asax.vb I have:
Sub Application_Start()
...
log4net.Config.XmlConfigurator.Configure()
End Sub
The directory (C:\temp\) where the log is supposed to be is Full Access for Everyone.
C:\>cacls C:\temp
C:\temp Everyone:(OI)(CI)F
BUILTIN\IIS_IUSRS:(OI)(CI)F
NT AUTHORITY\SYSTEM:(OI)(CI)(ID)F
BUILTIN\Administrators:(OI)(CI)(ID)F
BUILTIN\Users:(OI)(CI)(ID)R
BUILTIN\Users:(CI)(ID)(special access:)
FILE_APPEND_DATA
BUILTIN\Users:(CI)(ID)(special access:)
FILE_WRITE_DATA
CREATOR OWNER:(OI)(CI)(IO)(ID)F
The file is created and inherits the proper rights but remain empty while it is not empty on my development PC, using IIS Express.
C:\temp>dir
Volume in drive C is Windows
Volume Serial Number is 3A59-32AE
Directory of C:\temp
06/23/2021 07:18 PM <DIR> .
06/23/2021 07:18 PM <DIR> ..
06/23/2021 07:18 PM 0 inboundAPI.log
06/23/2021 07:41 PM 5,382 log4net.txt
2 File(s) 5,382 bytes
2 Dir(s) 15,342,981,120 bytes free
C:\temp>cacls inboundAPI.log
C:\temp\inboundAPI.log Everyone:(ID)F
BUILTIN\IIS_IUSRS:(ID)F
NT AUTHORITY\SYSTEM:(ID)F
BUILTIN\Administrators:(ID)F
BUILTIN\Users:(ID)R
IIS APPPOOL\InboundAPI:(ID)F
I have a system.diagnotic section in the same web.config file:
<system.diagnostics>
<trace autoflush="true">
<listeners>
<add
name="textWriterTraceListener"
type="System.Diagnostics.TextWriterTraceListener"
initializeData="C:\temp\log4net.txt" />
</listeners>
</trace>
</system.diagnostics>
That is writing to the same directory successfully and here is the content as it might help
log4net: log4net assembly [log4net, Version=2.0.12.0, Culture=neutral, PublicKeyToken=669e0ddf0bb1aa2a]. Loaded from [C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\inboundapi\7b262cab\40e772b2\assembly\dl3\b60f6c7c\739e9dfa_715cd701\log4net.dll]. (.NET Runtime [4.0.30319.42000] on Microsoft Windows NT 10.0.17763.0)
log4net: defaultRepositoryType [log4net.Repository.Hierarchy.Hierarchy]
log4net: Creating repository for assembly [InboundAPI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]
log4net: Assembly [InboundAPI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null] Loaded From [C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\inboundapi\7b262cab\40e772b2\assembly\dl3\df6af0be\ce6bcea0_5268d701\InboundAPI.dll]
log4net: Assembly [InboundAPI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null] does not have a RepositoryAttribute specified.
log4net: Assembly [InboundAPI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null] using repository [log4net-default-repository] and repository type [log4net.Repository.Hierarchy.Hierarchy]
log4net: Creating repository [log4net-default-repository] using type [log4net.Repository.Hierarchy.Hierarchy]
log4net: configuring repository [log4net-default-repository] using .config file section
log4net: Application config file is [C:\inetpub\wwwroot\InboundAPI\web.config]
log4net: Configuring Repository [log4net-default-repository]
log4net: Configuration update mode [Merge].
log4net: Logger [root] Level string is [ALL].
log4net: Logger [root] level set to [name="ALL",value=-2147483648].
log4net: Retrieving an instance of log4net.Repository.Logger for logger [inboundAPI].
log4net: Setting [inboundAPI] additivity to [True].
log4net: Logger [inboundAPI] Level string is [ALL].
log4net: Logger [inboundAPI] level set to [name="ALL",value=-2147483648].
log4net: Loading Appender [RollingFileAppender] type: [log4net.Appender.RollingFileAppender]
log4net: Setting Property [File] to String value [C:\temp\inboundAPI.log]
log4net: Setting Property [AppendToFile] to Boolean value [True]
log4net: Setting Property [PreserveLogFileNameExtension] to Boolean value [True]
log4net: Setting Property [RollingStyle] to RollingMode value [Date]
log4net: Setting Property [DatePattern] to String value [.yyyyMMdd]
log4net: Setting Property [StaticLogFileName] to Boolean value [True]
log4net: Converter [message] Option [] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Converter [newline] Option [] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Setting Property [ConversionPattern] to String value [%date [%thread] %-5level - %message%newline]
log4net: Converter [date] Option [] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Converter [literal] Option [ [] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Converter [thread] Option [] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Converter [literal] Option [] ] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Converter [level] Option [] Format [min=5,max=2147483647,leftAlign=True]
log4net: Converter [literal] Option [ - ] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Converter [message] Option [] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Converter [newline] Option [] Format [min=-1,max=2147483647,leftAlign=False]
log4net: Setting Property [Layout] to object [log4net.Layout.PatternLayout]
log4net: Type = [0], r0 = [.19700101], r1 = [.19700101]
log4net: Type = [1], r0 = [.19700101], r1 = [.19700101]
log4net: Type = [2], r0 = [.19700101], r1 = [.19700101]
log4net: Type = [3], r0 = [.19700101], r1 = [.19700102]
log4net: Searched for existing files in [C:\temp]
log4net: curSizeRollBackups starts at [0]
log4net: Opening file for writing [C:\temp\inboundAPI.log] append [True]
log4net: Created Appender [RollingFileAppender]
log4net: Adding appender named [RollingFileAppender] to logger [inboundAPI].
log4net: Hierarchy Threshold []
I think that I've read dozens of posts here and there and it might look like a duplicate but I swear that I tried all of what I read.
I still don't understand the following:
(1) Why is everything working on my PC with IIS Express?
(2) Why is the file created to suggest that rights are correct but remains empty?
(3) Why is the same IIS able to fill the log4net diagnostic in the same directory?
(4) Why is that diagnostic is not showing any error?
(5) Why is there nothing in the event log of Windows?
My brain is exploding!