This is an answer to the bounty rather than the original question. I think these are two different problems.
NitroxDM was experiencing Error Number: 18456, Severity: 14, State: 1.
State 1 now occurs when a login is disabled - but actually, the error
in the log is 18470, not 18456 - because the login is disabled, it
doesn't get that far. See state 7.
I think the process on the other machine had an incorrect password and was disabling the account.
Steinin is experiencing Error 18456. Severity: 14 State 8. Password did not match that for the login provided.
Probably the simplest of all: the password is incorrect (cASe
sEnsiTiVitY catches a lot of folks here). Note that it will say "the
login provided" even if you attempted to connect as a contained
database user but forgot to specify a database, specified the wrong
database, or typed the password incorrectly - unless it finds a match,
SQL Server doesn't have any idea you were attempting to use a
contained database user.
Both of these descriptions came from here.
I know you say you're able to connect with those credentials via osql. Either there's a case sensitivity issue, or SSMS has cached incorrect credentials. Try deleting or renaming
%AppData%\Microsoft\Microsoft SQL Server\[versionnumber]\Tools\Shell\SqlStudio.bin
and see if that helps.