The fact that you’re now experiencing this issue too has prompted me to do a little more digging. I have used 3 different Patreon accounts to create a dozen webhooks using the example code. Each webhook created for the first and second account has signatures that verify, however with the third account I have been able to create a webhook that fails signature validation: in fact, all 3 webhooks I have created with that account fail signature validation. The difference between the accounts is registration date: the third account was created later than the first two. The third account does have one webhook that (as far as I know) works – however, it was created 2 months ago. However, I have just registered a brand new account and signatures for those webhooks verify correctly – so I’m not sure if registration date is a red herring. When was your account created?
The issue appears to be that signatures generated for the webhooks of some accounts are not valid. You could try registering a new account to determine if it is indeed an issue specific to your account.
As the Patreon team didn’t seem to reply to the previous thread about this, I’d recommend reaching out to the Patreon team directly (via platform@patreon.com) to ensure that it doesn’t fall through the cracks.
I’m pretty confident there’s a bug with the Patreon system rather than the example code.