In 18.08 beta, I'm constantly being nagged by Google authentication dialogs for my gmail accounts. Every few hours an authentication window pops up for each account and I am required to authenticate.
This should be hugely improved in 18.08 final release and further improved in the next version. Make sure you also use your full email address as an username (incl. @gmail.com). Please reopen if this still happens in 18.08 stable and the full username.
Adding @gmail.com to the username fixes it, yes. However, I had backported 8e7dfb8696c8eb40c20ce46c532b2fcd10edf483 (which IIUC is supposed to fix this when not using @gmail.com) and didn't work.