I am a long time Pinterest user and I noticed today my site was now showing it was claimed any longer. I added the code to my header this morning, cleared caches, etc. and when I click to claim my site I get an error message. The error "oops we are unable to verify your website at this time."
Is this a bug? My site has been verified, but it has been a couple of years since I went into my settings to see if it remained verified.
I hope your problem is solved, but still if you are facing this error. I want to add value in your knowledge, in fact a few months ago I also made this kind of mistake. Had encountered and after much research I found my mistake. It so happened that I installed a new plugin in my Custom Printed Boxes website which deleted the code given by Pinterest.
When I removed that new plugin, my website showing claimed on Pinterest again.