It’s hard to say with the information provided, however, I will say that several of the issues with SPF records I’ve encountered are related to setup. Unlike the other records, you might add, there can only be 1 SPF record so if you have an SPF record for Google and need an additional one for HubSpot, the records need to be combined. Check the section on this page showing how to combine SPF records: Manage your email authentication
If that’s not the issue, please pass along more details.
i guess you are using gmail Pro for your company / users.
Can you check if it is still doing it if the user disconnect and reconnect his (or her) google acount from HubSpot ? It may come from here since your message could have only 2 solutions :
1/ the conection between the HubSpot user and Gmail is not “good”
2/ the way you send email with Gmail API use another software than HubSpot and is badly configured.