Hello Sebastian. I'd like to recommend a couple of quick steps on this that might help. First, make sure the SRS rewrite option is enabled under Settings>Antispam. Next, check your DNS server settings under Settings>General and make sure you can properly resolve the SPF records for these domains by way of those DNS servers. A quick test on the DNS side is to switch them out for Google DNS temporarily to see if the problem persists: 

If you find a domain you cannot properly resolve through your own DNS server (but can be resolved through Google) you know you have a DNS issue, and not an SPF issue specifically. Please let me know how you make out on this. Have a great day!

Hi Kyle

Yes SRS is enabled. Using Google DNS as well.

Thanks Sebastian, I appreciate you following up here as well. For the sake of documentation: Sebastian and I are currently troubleshooting these issues and it does look like the DMARC compliance check may be getting applied the the wrong addresses in some scenarios. We're working on narrowing down the exact situations that cause this so we can get development to take a closer look. We'll report back here when we know more. If anyone else has similar issues please increase your Delivery and Spam Checks logs to Detailed and submit a support ticket if possible.