Chrome Version       : 71.0.3578.98
URLs (if applicable) : https://photos.google.com/
Other browsers tested:
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari: OK - 12.0.2 (14606.3.4)
    Firefox:
       Edge:

What steps will reproduce the problem?
(0) Start with fresh incognito window.
(1) Go to https://mail.google.com/, login, wait for load.
(2) Open new tab, go to https://mail.google.com/a/appsdomainiown.com, login, wait for load.
(3) Open new tab, go to https://photos.google.com/
(4) Click top-right box to switch accounts

What is the expected result?
  Photos opens in second "appsdomainiown.com" account.

What happens instead?
  Photos goes to landing page or gets caught in a redirect loop because the login request for photos is unable to read any cookies. Attempts to get to the actual photos UI will always fail until cookies are removed or browser window is reset.

  chrome://net-export output says:

t=236659 [st= 0]   +URL_REQUEST_START_JOB  [dt=79]
                    --> load_flags = 18434 (BYPASS_CACHE | MAIN_FRAME_DEPRECATED | MAYBE_USER_GESTURE)
                    --> method = "GET"
                    --> url = "https://photos.google.com/login?pli=1"
t=236659 [st= 0]      COOKIE_GET_BLOCKED_BY_NETWORK_DELEGATE
t=236659 [st= 0]      NETWORK_DELEGATE_BEFORE_START_TRANSACTION  [dt=0]
t=236659 [st= 0]      HTTP_CACHE_GET_BACKEND  [dt=0]
t=236659 [st= 0]      HTTP_CACHE_DOOM_ENTRY  [dt=0]
t=236659 [st= 0]      HTTP_CACHE_CREATE_ENTRY  [dt=0]
t=236659 [st= 0]      HTTP_CACHE_ADD_TO_ENTRY  [dt=1]


COOKIE_GET_BLOCKED_BY_NETWORK_DELEGATE looks mighty suspicious as a likely cause of why the cookies are not being sent on the redirect to photos.google.com/login which is causing the redirect loop. But in an incognito window attached to a bog-standard gmail.com Chrome profile, there should not be interfering extensions.