[{"message":"An internal server error has occurred\nError ID: 605369606-244479 (119852647)"}]

Try this 

public class OPurchaseOrderFrontend {
 // Framework needs  {get;set;} set to write data
    @AuraEnabled public String AssetFunnel {get;set;}
    @AuraEnabled public Id MarketAccount {get;set;}
    @AuraEnabled public Boolean Active {get;set;}
    @AuraEnabled public Decimal TotalAmount {get;set;}
    @AuraEnabled public List<AssetFilter__c> filtersList {get;set;}
    // Explicitly defining the constructor so the serialization engine has a clear entry
    public OPurchaseOrderFrontend() {} 
}