Apple Mail Sync Delays

For some time now, I've has no issues with Apple Mail and Gmail syncing correctly between my MBP and my iPhone.

Recently, I have noticed a one-way sync delay (computer to iPhone) with emails that are read/deleted/etc not showing the changes on my iPhone. Everything works fine if I do something on my iPhone (i.e. the change is reflected in Apple Mail). It once worked flawlessly from the computer, now it barely works and I am stumped. I contasntly have to refresh the iPHone to show any changes done by Apple Mail.

Has anyone else experenced the same problem? If so, have you been able to fix the issue?

My thanks