I used this installer fix, but it didn’t help, I got wrong admin and database root passwords during installation (with default en_US locale). The password still contained characters that are not listed in the expression [A-Za-z0-9].
If the admin password can be changed by deleting mentions in the hestia config, then there are more serious problems with the database user, that is not so easy to fix.
Tested in Ubuntu 18.04 and 20.04