First of all thanks for making and sharing the video ... other than appreciating your enthusiasm it gives us a chance to be amateur and misleading coaches

.. jk ... really thanks for sharing ...
Here are my 2 cents based on first impression ... request to more advanced players to correct anything I say here , because I don't want to mislead OSPH here ...
1. You are reaching out for the ball in your TPB and that action is probably affecting your form on your SH Backhand blocks.
I am not sure if the technique for TPB is correct because I don't play penhold , but I would assume that forward motion should be a little smaller and you should let the ball come in a little more ... yes there is a forward component to the SH block as well but in my opinion it should be smaller and more of a follow through rather than the elbow unhinging in the forward direction so much to meet the ball. If I were you I would not practice blocking with SH at this time and only play the check mark loop.
2. FH issue , not much to tell from the video unless you show us your entire form along with the legs . I had this feeling that you are not bending your knees enough and making it up with bending it from the back .. but can't say that unless we see more FH along with the entire form ... and then again this is common challenge for amateur adults ... the knee bending part I mean ...