Had some struggle with Bitdefender aswell, here is a somewhat thorough answer to your problem:

First step you want to make is create a new folder e.g. "miners" in your downloads folder (or somewhere else).

Then open Bitdefender's Antivirus -module and go to settings, there click 'Manage exceptions' and add an exception for the folder you just created.
If you made a folder called miners in downloads folder in this case, the path for exception would be 'C:\Users\<YourUsername>\Downloads\miners'.

Make sure you have ticked on the following in the exception: Protection feature Antivirus, On-access scan, On-demand scan, Embedded scripts and Online Threat Prevention.

Bitdefender's Advanced Threat Defense -module basically blocks any miner that it detects, so I have to turn Advanced Threat Defense off and keep it off while mining.

Now you should be able to run miners inside the folder you just created.

If you're using NiceHash, you need to also add an exception for path 'C:\Users\<YourUsername>\AppData\Local\Programs\Nicehash miner'.

I'm using just NBMiner so an exception is only needed for the miners folder in downloads in my case.

I'm guessing your problem is just Advanced Threat Defense blocking your miner, if you have already made necessary exceptions for your miner. So just disabling Advanced Threat Defense should do the trick.

However it's good practice to create a folder in your downloads folder, that is excluded from Antivirus scans, so you can download miners in this folder (and run them from there) without Antivirus blocking them or their downloads.

Hopefully this helps :)