The past few days, my internet browsing has become very poor. It's not a matter of speed, as a speed test will give at least 15Mbps. It seems as if my laptop has a hard time actually connecting to the sites.

I've found a possible culprit, but don't know why it would affect anything:

Going to adapter settings and disabling ipv6, but leaving ipv4, my browsing is back to normal. Re-enabling ipv6 brings back the issue. This is strange though, because I have always had ipv6 enabled. Moreover, using sites to test ipv6 compatibility, I fail with ipv6 enabled on my adapter, and pass when it's disabled.

Ideas about why this is happening, and how to fix it?