There is a bug in Omada Controller 3.0.2: it does not allow device passwords which contains non-alphanumeric characters as seen in the screenshot below.

You might now ask what's the problem if certain characters are not allowed in passwords?

The problem is that previous versions of Omada Controller up to v2.7.0 did allow such characters in passwords and if you copy your existing database from v2.7.0 to v3.0.2, the passwords are silently imported into the v3.0.2 database. Result is that one can't change device passwords anymore if an old password from v2.7.0 contains special characters.

Note that the password in the screenshot below is the current password - you can't correct it since it must match with the password in the database to do so.

BTW: as a general rule, passwords should not have a restriction to alphanumeric characters.