Why can't I save GIFs from sensitive tweets?
When a tweet is marked as containing potentially sensitive content, Twitter doesn't embed any media-including GIFs-in the public-facing website until after the user acknowledges that the content may be sensitive, and that they still want to view the media.
This is done by first presenting a warning, along with a button that allows the user to bypass it and view the tweet's content.
GIFwrapped isn't able to bypass this warning, as the engine used to find GIFs within web pages is not built to enable interaction with them.
Even if it were, Twitter's website is specifically written to obscure the button from web crawlers, meaning that it wouldn't be able to find the button in the first place.
As such, it can't bypass the warning, and the GIF is never made available... so GIFwrapped can't download it.
Why have I never seen this warning?
Twitter offers the option to display all media that may include sensitive content. This can be enabled from Twitter's account settings, but only affects media viewed when that user is signed into their account.
GIFwrapped uses an ephemeral web session for accessing web pages, meaning that it doesn't cache content or store cookies. This is similar to a private browsing session that is possible in many major browsers.
As such, it's not able to sign into an account, and it certainly doesn't have access to the account used by your preferred Twitter client (even if that client is Safari). Ultimately. this means it always encounters the warning, even if you don't.
Who decides what is sensitive?
Twitter does, and they have a detailed policy by which they determine what is sensitive and what is not.
GIFwrapped doesn't impose any additional restrictions on downloading GIFs from Twitter. If the tweet can be accessed by GIFwrapped, and it has a GIF attached, the GIF will be available for download.
How can you tell a tweet is sensitive?
It's an educated guess.
GIFwrapped looks at each tweet on a page individually, and if no GIF is found for that tweet, it looks for the link that would normally allow a human to change their settings. The link isn't of any use to GIFwrapped (because it requires users to sign into their account), but its presence indicates that the tweet is likely considered potentially sensitive.
Using this logic, GIFwrapped can display a special error that indicates why it can't download the GIF, but there's no way to use it to actually access the GIF.
When will a workaround be available?
Probably never. Twitter is far more likely to further restrict access to these GIFs than it is to ease the restrictions, so it's only going to get harder for GIFwrapped to access them.
Furthermore, as a solo developer with extremely limited time and resources, I'm not able to commit to finding ways around these restrictions.