Error occurred during a cryptographic operation - Schedule not working but Script

Product: PowerShell Universal
Version: 5.5.3

Hi everybody,

I have a weird thing about Schedules and Scripts: in the Schedule I get the error
Error occurred during a cryptographic operation.
Nothing more, also in the logs not showing any exception.

The script I am scheduling is working itself, so when executing it manually it works as desired, just the schedule not.
Regarding “Crypto”, I am using some String Secret that is passed into a local variable as SecureString as $ClientSecret is a possible, optional parameter:

if (-not $ClientSecret) {
    $ClientSecret = (ConvertTo-SecureString $($Secret:SECRETSTRINGVARFROMPSU) -AsPlainText -Force)
}

I checked all other posts on this error, but there is nothing really up to date

Best,
Matthias