There are scores of folks complaining of this problem going back a couple years. Almost all of them are talking about streaming sites or porn sites not working on an Apple device.
Given the time frame of all the complaints and after reading through a couple threads, I'd say this looks like a thing that happens somewhat regularly, albeit not to all users, and often and seems to resolve itself in a matter of time. That is consistent with Apple pushing updates to alter or block certain elements (sketchy video players for example) on their devices in order to cut down on illegal streams (Apple has its own streaming service after all), and then the folks running the sketchy websites need to update their software to get around the new "fix." This same game of whackamole happens with Youtube and uBlockOrigin all the time.
Apple is the most walled off operating system there is, and so they have a ton of control over your device. As such, there doesn't seem to be much you can do here outside of jail breaking your iPhone and then knowing how to disable whatever it is they are doing.
Your options appear to be: 1. buy league pass, 2. use a non-Apple product, 3. wait and hope it fixes itself, or 4. roll back your OS to a previous version where you didn't have this problem.
Personally, I would do 1 while 3 happens and then plan to do 2 before next season.