I have exactly the same. I noticed it is not just gmail, some other gsuite stuff too.
Anyway, mail loads as per normal, you get the list of emails etc. yet, it shows on the tab that is still loading and nothing is active. I can't click on anything. It is like an image.
After sometime chrome brings up unresponsive page message. Refresh, reload etc. nothing helps, yet works in incognito just fine.
I had the same with Drive and calendar. Sometimes, when I start a new tab or window it runs fine.