In general, there are three ways:
1. You send me a project and I debug it, fix the error on my side, or show you the error on your side.
2. I connect to you using TeamViewer or AnyDesc, and try to debug this on your side.
This is very inconvenient for me and for you, and requires discussion to schedule the time of the call, because you and I are in different time zones.
3. You debug it yourself. The difficulty and time of debugging depends on your programming skill, the complexity of the error, and your luck.

Are there any other alternatives? This support request was simply to speed up the process of manually debugging the script(s). If there are none, that will be my next step. Thank you for the help so far

375: if (texture != null)
376: {
377:     if (map.control.resultIsTexture) _colors = texture.GetPixels32();
378:     _width = _textureWidth = width ?? texture.width;
379:     _height = _textureHeight = height ?? texture.height;
380: }

Line 379 is equivalent to the following line:

_height = _textureHeight = height != null ? height.Value : texture.height;

This means that only texture can throw a NullReferenceException.
But, the texture cannot be null, because this is checked on line 375.

Please send me your project by email (support@infinity-code.com). I will check it.
To make it clear:
I don't need your working project. I need any temporary project where the problem is appears.

Your exception has a strange line.
Which version of Online Maps are you using?

NullReferenceException: Object reference not set to an instance of an object
OnlineMapsMarker.Init (System.Nullable`1[T] width, System.Nullable`1[T] height) (at Assets/OnlineMapsV3/Online maps/Scripts/Markers/Instances/OnlineMapsMarker.cs:379)

This is the exact error. I use the following method to create markers with two different filters:

public void PlaceMarkersOnMap(string eventTitleFilter) {
      markerManager.RemoveAll();
      foreach (MarkerData data in MarkerDataManager.Instance.MarkerData) {
        foreach (EventAtLocation eventAL in data.HostedEvents) {
          if (eventAL.EventType == mapType) {
            if (eventAL.EventTitle == eventTitleFilter) {
              markerManager.Create(new Vector2(data.Longitude, data.Latitude),
                markers[GetMarkerFromName(eventAL.EventTitle)],
                data.UID.ToString());
            }
          }
        }
      }
      this.gameObject.AddComponent<MarkerTouch>();
    }

This is the only method that controls marker creation. Can anyone identify this problem and recommend a solution? Thank you for the help!