Append queries not working correctly

If you can see all the data in the Data view, that would suggest the Append' has worked correctly.  Can you confirm this please?

"When I make a filter it shows both tables data, but when I filter it to the second tables data the table goes blank" -> this suggests that the filter on the second table is not doing what you expect it to do.  

Here are some options:

Attach the pbix and I'm sure someone can sort it for you reasonably quickly.

and/or

Investigate why the filtering of the second table is not working.  This could be some data anomaly (hidden characters etc).  What kind of filtering are you using? What's the data type involved?

You could try filtering in Data view using the column dropdowns to experiment.   You could post pictures of the filtering to show us what works and what doesn't.