Gmail calendar invites not showing in Inbox

I have been having a really annoying problem on iOS for sometime now whereby if my partner sends me a meeting invite to my gmail calendar (gmail account is bound to my iCloud account), the invite arrives in the calendar app inbox on iPad Pro, MacBook Pro, Apple Watch but not on my iPhone X!

I have the Google account added and the calendar turned on and set to be my default on my iPhone and have tried removing the google account completely then re-adding it, checked notification settings etc all to no avail. If I go into Calendar and browse to the day when the meeting is on, I can see blocked out time with the meeting and I then get the option to accept decline, but not unless I go through day by day and check it. Has anyone seen this before and fixed it? This has been going on at least since iOS 10 and I'm now on iOS 11.2 beta.