I use @Ekpu tips referenced in #22 post, and it works easily!
cd /var/www/wallabag2
bin/console --env=prod fos:user:change-password
Please give the username:myusername
Please enter the new password:
Changed password for user myusername
I set the same password that I used before the problem, and login is back!
I updated issue#217 also.
Remaining problem is: I did it for only one user…