Sites that require phone number verification often block numbers allocated for VoIP services for fear of spammers. YMMV if you've tethered your GV number to a physical device at some point.
I've run into this semi-frequently over the years, and it's always extremely frustrating when it happens, but somehow I can't remember exactly where either.
I can back this claim up. I was unable to verify my Citi credit card over the phone using my Google Voice number, they insisted on a non-VoIP number which ultimately delayed the verification process by a week.
I don't remember honestly, but I was looking for a site to do my taxes when I saw the last one. I didn't finish signing up. It mentioned not supporting "voice over IP" numbers, or something to that effect. I wish I'd taken a screenshot.
It used to happen for me on Telegram (I think it's been fixed within the last year though), and recently a startup (Mealplan) blocked it because it's a "voip" number. I even tried emailing and explaining, but they just said they don't support it.
Microsoft won't take any known voip account for an Azure registration, which created a minor challenge for me as all my numbers are google voice only as well.
Mind sharing where? I've use my Google Voice number exclusively for 6 or 7 years now. Can't say I've ever ran into such a thing.