Hi Janine97,
Supplier payment terms shouldn't change on their own, but there are a few reasons why this might be happening.
It could be someone on your team is updating them, possibly without realising the impact. Another possibility is that the terms are being changed automatically when bills are imported or updated through a connected service or integrations.
If the issue is still happening after checking these things, reach out to our live chat support through our virtual assistant MOCA or submit a case via MyAccount so they can double-check everything for you.
Regards,
Sai