Very strange admin login loop after failed 1-click upgrade 1.7.7.1->1.7.8.11 and back-up

[Yulia T.]

Dear community,

I've tried to upgrade from PS 1.7.7.1 to 1.7.8.11 with 1-Click App. However upgrade failed  so I tried to  back-up to the same condition as before upgrade (both, PS and DB). There were many problems, but as a result the frontend runs, however no orders can be made. And I can't log-in to my backoffice. Once I put my login and password  it comes back to login page.

I've tried to clean cache, to use other browsers, I've put PS_COOKIE_CHECKIP = 0, but nothing helps. And it's definetely not a hack.

I noticed, that after every failed login one row is added to the table ps_employee_session with id_empoyee_session=0. All the rows from backed up table have normal id's (s. attached screenshot).

DB is MySQL, PHP 7.2 for DB, PHP7.3 for PS

PS ran before upgrade with no problems. The only reason for upgrade was that I've received several fake customers daily and hoped to fix this issue with the newer PS version.

I'm fighting with this problem since many days and have no success. Maybe somebody has an idea? If possible, please not too short advises as I'm not professional programmer 🙂

Thanks a lot in advance.

Yulia