Thanks for filing the issue!

Unable to reproduce the issue on reported chrome version 71.0.3578.80 using Ubuntu 14.04 with the below mentioned steps.
1. Launched Chrome 71.0.3578.44
2. Signed into a Website/Webpage(....Amazon)
3. Upgraded chrome to version 71.0.3578.80 from version 71.0.3578.44
4. Launched upgraded chrome version 71.0.3578.80
5. Tried opening Amazon page.
We were able to see the page signed in.

@Reporter: Could you please let us know if we have missed anything in the process. It would also be helpful if mentioned, if this is specific to any particular page.

Hi, thanks for the reply and Happy new Year! :)

Ill run through my own experience: See an update is ready. Close all my
applications, run the update. Afterwards I find that I need to log back
into Chrome (its usually already logged in when I start it) and going to
various websites, Amazon included, but NOT ALL websites, I need to re-type
my user name and passwords. I also find that for the next two or three
times I open Chrome I need to log in each time - this stops and I remain
logged in after several of these, and I then find that most of my website
logins are fine again. Its almost as if it gets stuck in a logged out mode
until I have restarted it a few times.
This has happened quite a few times now, enough for me to start bleating on
about it (because it IS really annoying!) and Iv tried restarting the PC
(including a full power off) but it seems to make no difference, even if I
restart directly after an update. For at least two or three restarts of
Chrome, Ill have to log in as the user and my website logins are broken,
and then, suddenly, Ill start Chrome, already be logged in (as usual) and
the websites will work again.
Sorry its not a more informative answer, but that really is all of it. Its
most odd (and quite annoying!).
Feel free to make further contact if it will help - Chrome is my default
browser and has been for a long time so I'm fine with helping address this
issue.
Regards
Huw

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Can you open chrome://histograms/ and find PasswordManager.LinuxBackendMigration.Adoption? What is the recorded value?

Do you see your passwords in chrome://settings/passwords? Do you see them in the Keyring (you need to install seahorse app)? 

Thank you for the information.
Along with information from comment 8, could you let us know if the issue reappears if you reboot your machine, while the issue appears to be fixed?

Hi. When an update first triggers this issue a machine reboot does not seem
to fix it. In fact it *seems* that it is more about the number of times the
browser is closed/opened than the state of the machine itself. This issue
appeared on the last update but once it has "fixed itself" everything is
fine again until the next update.

Histogram: PasswordManager.LinuxBackendMigration.Adoption recorded 1
samples, mean = 0.0 (flags = 0x41)

Do you see your passwords in chrome://settings/passwords?
Yes. Passwords always appear to be present even during this issue.

Did I understand right that the relevant passwords are present in chrome://settings/passwords but they are not autofilled?

In this case please open chrome://password-manager-internals/ and then open another tab with Amazon (or any other problematic site). After waiting for a few seconds with the login form open, you can copy/paste the log here.