Auctiva will be implementing the new return policies.
According to eBay's developer information for Simplified Returns:
We understand that some applications depend on API metadata to support return policies. Therefore, the API will continue to accept listings with a 14-day return policy through late August, to minimize interruptions.
You can find the full document here.
Auctiva does depend on eBay's API metadata to determine what should and should not be available per eBay site and category. Until eBay updates their API to return the new information, we are stuck with what we have.
Until then, please know that while your listing might generate warnings from eBay, it should not prevent you from listing. eBay's plan going forward is to automatically move the return information up to the next closest option once their changes are mandated.
For example, someone with 14 day returns selected would see their listings changed to 30 day. The listing should not be taken down.
I hope I have explained this well and that it helps. eBay certainly is making a lot of changes lately!