I’ve had this happen also with certain pages and I believe it’s Google incorrectly crawling the site.
Use Google Search Console to re-inspect the URL/s and if/when Google detects that it’s ok, you can re-submit it for indexing.
I’ve had pages that definitely don’t have any robot meta tag and Search Console has still reported them as having a ‘noindex’ set. Sometimes has taken a few attempts to get Google to re-inspect it correctly.