Like other users here I have been having issues with the Pinterest Save Button working off and on but with increasing frequency over the last few months. I've been in contact with their Support Team over the last week, but like others have mentioned, they don't seem too keen on actually fixing the issue.
The 1st person gave me a list of things to try, despite my having stated that I had already done so, & wanted me to send video as proof that I had done them. I sent screencaps & a more detailed description of the issue, including that there is a second account on the same computer, using Pinterest in the same manner, that is also having the same problems but didn't develop them at the same time/rate.
I was passed off to another member of the support team who seems to be convinced that I'm just not logged in, despite the screencap showing both my being logged in & the failed save screen in the same shot. They sent me a screenshot of them being logged into my account & successfully pulling up my boards as if they were going to pin a site, but when I went to do the same my boards ceased to exist in the pop-up (& yes, I was logged in. . .).
I don't know what the malfunction is, but apparently enough people are being effected that they need to make a mass announcement that it exists & that they are looking into it, then actually look into in instead of sending the same failed "solution" to the same people repeatedly.
They decided, without telling me which browser or devices they were using that didn't recreate the problem, that they were done with me & closed my inquiry. So for anyone else that wants to contact them, make sure you find out what they're using to try to diagnose the issue.