MDB Post-processor Error: "Object reference not set" Despite Correct Configuration & API Key Validation

Hello dear community,

I'm facing a persistent issue when using the MDB post-processor with WebGrab+Plus (version 5.3.0.0) on Ubuntu 24.04. My goal is to grab EPG data from tvtoday.de for the DMAX channel and then enrich it with additional information (season/episode) using MDB.
My System:

Operating System: Ubuntu 24.04 (Kernel 6.8.0.60)
WebGrab+Plus Version: V5.3.0.0 (with MDB & REX Postprocess)
.NET Runtime: Environment: 8.0.17 (specifically, dotnet-runtime-8.0 was installed after the app initially found dotnet-runtime-9.0 and indicated a missing 8.0 version).

The Problem:

The WebGrab++ grabber itself runs successfully, retrieving EPG data from tvtoday.de. The license is also recognized. However, immediately after the grabber job completes and the MDB post-processor starts, I receive a Critical error:

[ Info ] Job (MDB Version: 3.4.1) started at 16/06/2025 11:45:43
[Critical]
Object reference not set to an instance of an object.
[Critical]
at .–. ..ctor(String)
at .–. ()
at .–..ctor(String[])
at .—. (String[])
[Critical] Unhandled Exception
[Critical] Execution stopped

This error consistently occurs, even before MDB actually starts matching shows. The MDB portion of the job completes in only 0-1 seconds, suggesting it's not even initializing correctly.
Troubleshooting Steps Taken So Far:

WebGrab++.config.xml:
The WebGrab++.config.xml has been thoroughly checked and adjusted for correct syntax. Currently, the MDB post-processor is configured as mdb, as expected for using an external mdb.config.xml.
Current WebGrab++.config.xml:
XML

<?xml version="1.0" encoding="utf-8"??>./guide.xml!,m,nmdbrexMozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36 Edg/91.0.864.59To force a license update; replace this text with the letter fon41iDMAX

mdb.config.xml:

The mdb.config.xml is located in the same directory as WebGrab++.config.xml.
The XML structure was checked for syntax errors (episode, missing opening tag) and corrected.
It was most recently re-created as plain text with UTF-8 encoding (without BOM) using nano to rule out encoding issues or invisible characters.
Current mdb.config.xml:
XML

<?xml version="1.0" encoding="utf-8"??>true100episodeYOUR_TMDB_API_KEYde

API Key Validation:
The TheMovieDb (TMDb) API Key (v3 API Key) used in mdb.config.xml was manually tested via curl and is confirmed to be valid and working correctly. The request returns proper JSON results.
Example: curl "https://api.themoviedb.org/3/search/movie?api_key=YOUR_TMDB_API_KEY&query=Interstellar&language=de" returns valid movie information.

.NET Runtime Environment:
Initially, WG++ was trying to run on .NET 9.0 but requires .NET 8.0.
dotnet-runtime-8.0 has been successfully installed. The log now shows Environment: 8.0.17, indicating the correct runtime is being found and used.

File Permissions:
Read permissions for mdb.config.xml have been checked and appear to be sufficient for the user running WebGrab++.

Summary of the Issue:

The "Object reference not set to an instance of an object." error occurs directly at the very beginning of the MDB post-processor's execution (after the Job (MDB Version: 3.4.1) started message), before any actual show matching takes place. Since the configuration (XML structure, API Key) and the .NET environment have been ruled out as causes, we suspect a deeper issue with the MDB component itself or its initialization process.
Question to the Community:

Has anyone experienced similar issues, or do you have any ideas what could be causing this error when the configuration seems correct and the API key is verified to be functional? Is a reinstallation of WebGrab++ the next logical step to rule out potential corruption of the MDB files?

Any help would be greatly appreciated!