This is an issue with all popular VPNs on various websites. VPNs use shared IP addresses so just a few bad actors using that VPN can get it blocked for everyone. I can't even load Google sometimes without multiple human verification checks.
Let's not pretend it's all about "bad actors". They don't want masked traffic at all, the "bad actors" gives them an excuse.
And we know this because if the IP was the issue, they wouldn't let you use the site at all, but they will work fine after signing in. Any of these VPNs work as long as you're logged into reddit, even with a throwaway account.