I have a personal VPN running OpenVPN 2.3.10 on ubuntu 16.04 that I installed following this guide. It has worked with some setbacks in the last two months of intermittent use.
Yesterday, I tried to go to Reddit on my MacBook (OS X 10.14.1) using Safari and I get an error that says OpenDNS is filtering the forums for my IP address. I also receive several "unsecure connection" warnings and other warnings about possible attacks by intermediaries on websites I had never visited. So it's not likely that I'll just set some funny security exceptions for Reddit that have already expired. They are not all websites, but I can not find a pattern, except those that are explicitly filtered for some reason.
The VPN runs on a computer in a network with regular users (ie, their own computers) who have no problems getting to Reddit (or other websites). So the problem is likely with the VPN itself. For example, it is not the case that OpenDNS is really blocking the traffic to my IP because all the users of the network have the same IP against the Internet and have no problems.
A user within the network (who also uses a MacBook) has no problems getting to Reddit (use Firefox, if it is important) while using the network normally. If you connect to the VPN from within the network, you have the same problems as me. I have iOS devices that use the VPN too, and they also have this problem. I can also use VPN Unlimited without this problem, which indicates that it is a problem with my VPN and (perhaps) with Apple devices.
Looking for solutions to this problem, I found this website that tells me to add a certificate called "UCA root" from Cisco Umbrella to my keychain and then set it to "Always reliable".
This seems to have solved the filtering problem on my MacBook. Editing: this is not true, I do not know why it seemed to work for a while, but it does not work anymore.
Since all the devices that I have had problems with are Apple products, I suppose Apple has implemented some type of security update recently that has caused this problem, but it is also very likely that something has expired in my VPN. I would like to know why this happens all of a sudden and if there are any changes I can make to the VPN server to fix it on all my devices.