The reason is "messages on the web" is running through "messages" on your cell phone.
After a week with the p40 pro I've got most problems worked out. Transferring photos from "Gallery" is still a nuisance and there is no way to use my chromebook to type responses to messages I receive on my phone. I'm running four apps off the web: Google Keep, Calendar, Contacts, and News. Lastly a couple of apps I paid for through Google Pay aren't recognized as paid by Huawei.