SES Sending from Unapproved IP

We use SES for sending emails and we recently received some from a batch of emails that were delivered with an IP address that isn't part of the SPF record for amazonses.com (and were therefor bounced).

Emails were received from the below IPs in the same batch, but the first one is not part of the SPF record.

104.47.61.50 54.240.48.30

https://mxtoolbox.com/SuperTool.aspx?action=spf:amazonses.com:104.47.61.50

Was this just a once off issue or out of date SPF records?