Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
This is a known issue with El Capitan.
Can you try on a machine running a different OS and let me know if it works ok?
That is one workaround, another would be to use a different coloured background.
I am a user of this site just like you, I have nothing to do with the payments.
From reading your initial description, the hyperlink is not visible in a browser, but still exists - does it appear as white text on a white background, making it invisible?
Do you have a link to the website?
Do you have a link to the website so I can see the problem more clearly?
Ok, cool site! I see the problem with the hyperlinks more clearly now.
Is this only happening with new links that you add to the site?
Is it only happening with some button types?
Ok, an option may be disabled or turned off..
Check the main menu iWeb > Preferences... and make sure that the third option 'Show text imaging indicator' is switched on.
Or you could try linking only the text, not the text box.
If a background is needed, try using the color fill option, not the background fill.
If the linked text is over an image that is also linked, undo the image link.
If the link still disappears, try changing the font.
Ok, then iWeb is definitely not performing as it should when used with El Capitan!
I expect they are working on a fix for this glitch.
In the meantime, you have found a great workaround for this problem.
I mean Apple should be working on a patch for El Capitan to reduce the conflict between OS X and any legacy apps.
Are you considering updating to Sierra?