Using Gmail with outlook and having issues when synchronizing

Hi Guys

I have been using Gmail through Outlook 365 for quite some time, however until recently (last few weeks) I have been experiencing issues when synchronizing subscribed folders, which sometimes results in delay in receiving emails and sending out (occasionally it gets stuck in outbox and sending out repeatedly). I have did some research and set up my 2-step verification already, however the issue remain the same. The current usage on my Gmail is only around 3GB, so believe not the reason of cause. Just wishing to see if any other has the same issues and how you've manage to fixed it.