Error when Importing MSOnline Module as part of a background script

Hi Folks,

I'm struggling with one of our PowerShell scripts. The controller script calls a function which does something in the AAD.

The top of the function looks like this:

function Set-WpAzureMFA {
    [CmdletBinding()]
    param (
        [Parameter(ParameterSetName = 'Identity',
            Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [string]
        $Identity,
        [Parameter(ParameterSetName = 'Path',
            Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [string]
        $Path,

        [Parameter()]
        [ValidateNotNullOrEmpty()]
        [System.Management.Automation.PSCredential]
        $Credential,
    
        [Parameter()]
        [switch]
        $Enforced
    )

    begin {      

        try {
            Write-WpCoreLog 'Importing module MSOnline.' -Script
            Import-Module -Name 'MSOnline' -ErrorAction Stop
            Write-WpCoreLog 'Initiating a connection to Azure Active Directory.' -Script
            Connect-MsolService -Credential $Credential                
        }
        catch {
            Write-WpCoreLog -Message 'An unhandled exception was thrown.' -Script -Level 'Error'
            $PSCmdlet.ThrowTerminatingError($PSItem)
        }
    }

The error occurs within the line of 

Import-Module -Name 'MSOnline' -ErrorAction Stop

The exception throws: 

Import-Module () : Unable to cast object of type 'System.Boolean' to type 'System.Collections.ArrayList'.

Maybe someone has an idea what could be wrong. The script ran fine for months and now it throws these errors.

Thank you in advance!