my bad, i meant captions when i said comments
captcha has nothing to do with this, if you were hit with captchas, you couldn't do anything until you solve them, let alone uploading pictures
it's the content of your caption for sure, it might look innocent to you, but it gets filtered by ig, they suffered from a lot of abuse, so they tightened their security maybe a bit too strict to the extent when it affects the everyday user experience negatively
i cannot really say anything else to you than what i already recommended above: try to re-word your captions and see if that helps, switch up hashtags, mentions if there's any