Filtering column data while using Custom Data Server results with error

Hello,

After my last support ticket, I have implemented a custom data server solution for my project based on your example from here:

https://www.flexmonster.com/doc/pivot-table-with-dot-net-core-server/
https://www.flexmonster.com/doc/introduction-to-custom-data-source-api/
https://github.com/flexmonster/api-data-source

Till now everything worked fine, although I had to adjust some parts of your code in order to pass necessary data needed for my custom data source to work properly (but nothing out of ordinary). Recently I encountered an issue when trying to filter the data inside the columns, it fails and does not really throw any significant exceptions during code execution, but only while parsing the data for 'select' http request (my guess based on what I have found). The only meaningful error message I could get is from scanning the network traffic and here's what I got:

1. errors: {query.filter[0].exclude[0].member: [,…]}
   1. query.filter[0].exclude[0].member: [,…]
      1. 0: "Error converting value 1579046400000 to type 'OCT.Flexmonster.Models.ValueObject'. Path 'query.filter[0].exclude[0].member', line 1, position 418."
2. status: 400
3. title: "One or more validation errors occurred."
4. traceId: "|13d9b65b-4b432e48ec37de43."
5. type: "https://tools.ietf.org/html/rfc7231#section-6.5.1"

At first I thought it might have been related to some kind of data value parsing, but after trying to filter out plain 'string' values I also got errors like these:

Error converting value \"Account 100\" to type 'OCT.Flexmonster.Models.ValueObject'. Path 'query.filter[0].exclude[1].member', line 1, position 426." 

The filtering I'm taking about is simply executed by the UI (I've included some screenshots in the attachments). 

To help you out narrowing down and debugging my problem, I've included every parts of the code that could be relevant to you (see the attachments for 'code.zip). Here I included my custom data source / server implementation on the net backend side as well as angular component with everything set up (some parts may be missing, but you should be able to get the whole context of my use case).

Any help will be appreciated.

Best regards,