Hello Thomas,
I understand the inconvenience caused. I am sure we will be able to fix this together. In this case, I request you to reinstall AVG Online Shield component once (please open AVG Internet Security > menu > settings > components > uninstall Online Shield), reboot your computer once. After reboot, please go to the same path and install online shield. I also request you to change AVG Firewall network profile to private (open AVG Internet Security > menu > settings > components > firewall > customize > network profile > change all the network public to private), please go to Firewall customize settings again > scroll down > click on system rules > enable all the system rules if it's not configured, please click OK and check if you can access the same download speed with enabled AVG Internet Security.
Best regards,
Alok.
Hello Thomas,
I am sorry to hear that the issue persists. Please run AVG repair avgclick.me/RepairAVG from your computer control panel and check if that fix the issue. If issue persists, please reinstall AVG completely from your computer. You can install latest version of AVG Ultimate from this link: http://support.avg.com/SupportArticleView?urlname=Download-and-install-AVG-Ultimate. If you face any difficulties, feel free to contact us.
Thomas,
I would like to appreciate your efforts and patience so far. I have sent you an email instruction to get connected with our technical support team. Please follow those instructions to get in touch with them and you should be able to resolve your issue.
It didn't help 
the same issue is happening on my second PC that also has AVG.
Hello Alok! Thanks for your reply. Sadly it didn't fix it the issue.
It didn't help the same issue is happening on my second PC that also has AVG.