This is related to this FAQ:

https://www.paypal-knowledge.com/infocenter/index?page=content&id=FAQ2067

Basically the root of this is that from Jan 17th any variable or data sent to PayPal in the HTML form will not be supported. So anything not documented HERE will cause an issue post Jan 17th

Happy to help troubleshoot specific buttons if you want to post links to buttons you are concerned with. A good way to test is to click the buttons, if the checkout page visible is the new checkout flow, then the button is fine. If you see the old checkout flow it needs work.