THIS IS NOT A DUPLICATE OF SIMILAR QUESTIONS (like this)

I just had to write that first, there are tons of questions similar to this, all of them have the same redirect to an answer that does not solve my problem, because I don't have the same problem, just the same symptom.

I write tests for my companies application. One of these tests tries to upgrade the application from a previous version to a new version to make sure nothing breaks. When I am installing an old version of the application, some weird stuff starts to happen.

Sometimes everything goes Okay, and nothing is wrong, other times when trying to install I get this message (company app name censored):

E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/XXX-amd64_Packages
E: The package lists or status file could not be parsed or opened.

Using the solutions provided in the questions similar to this one (like this). Do not help, and the problem keeps repeating itself once it happens the first time.

This has led me to believe something is wrong on the apt server where the package is being created, but searching these errors yields no information on anything beyond the "fix" suggested in the question I linked, the only other source of information I could find also did not help (here):

So I am asking for information;

• What is the actual problem?
• What causes the problem?
• What can fix the problem?

I hope this question is in good format, if there is a problem, or missing information I can move to chat.