It's probably blocked by Windows Defender then. Blame MS for that.
I disabled Windows Defender too and all its damn modules. I found the solution, though, so I write here to help those who could be in the same situation. It's Microsoft to blame, yes, but for another reason than Windows defender (Windows 10 October Update).
The problem lies with the Windows 10 October Update, the one that Microsoft blocked after finding it could delete all files in documents folder of the users but that, in my case, installed prior to Microsoft deciding to block its distribution (I didn't lose any documents, but I couldn't revert either to pre-Windows update because my backup software - Macrium - had created on Sunday a new full backup, including the infamous October Update by Microsoft).
After debugging in the past 2 days and trying all sorts of things, I noticed that none of the Assetto Corsa plugins worked, amongst those that used to read and write to the "Assetto Corsa" subfolder under main "Documents" folder of my account. This led me to suppose that some permissions of the "Documents" folder were set in a wrong way by the October Update, even though the permissions seemed to me ok (I was the owner of my "Documents" folder and I had "Total control" over it).
How did I solve? By luck, indeed. In fact, to exclude any virus or malware from my system preventing plugins to work, it happened I had installed Eset Total Security, trial version. The scan revealed the PC was clean but I noticed, in the Eset Total Security options, a tool that promised to check Windows for post-installation problems. I ran the tool, included in the aforementioned security suite, and it warned me that some system folders (it didn't tell me which) had wrong permissions, different from the default ones. I asked Eset to repair the permissions and it reported me that the operation was successfull.
Afterwards, I installed again ptracker, I received an error at the end of the installation telling me that ptracker could probably be blocked by the antivirus (now, Eset), but I simply closed the installation folder and ran Assetto Corsa withouth creating any exclusion for ptracker.exe in the security suite.
Well, Assetto Corsa started and this time, after entering the cockpit of my car, ptracker was fully working. Assetto Corsa logs are now reporting that ptracker and the other plugins CAN read and write the "Assetto Corsa" subfolder under "Documents" folder of my account. So, STAY AWAY FROM WINDOWS 10 OCTOBER UPDATE, because it messes system folder permissions (probably, an issue related to the update deleting files and folders of the account, by the way).
TL;DR: if you installed Windows 10 October Update prior to Microsoft blocking its distribution and Assetto Corsa plugins don't work anymore after the installation, uninstall every security suite you have on your system, install Eset Total Security (trial version), run the tool to "check and optimize the system", let it repair your system folder permissions and Assetto Corsa plugins will start working again!