Failing at making "Fast Mozzarella"

Looks like the rennet is missing in your recipe. You also might want to consider to skip the shortcuts and the vinegar and to start off with a more authentic/original formula as you usually can assume that each step and ingredient in them is there for a reason.

Your post was a bit confusing, because you say your recipe is for mozzarella but then you say...

I tried making ricotta and paneer in the past and it worked flawlessly. I have another 1.5L of milk available and I would like to succeed with that at least.

..which I interpreted as meaning you were making ricotta, not mozzarella.

Your recipe does not work for mozzarella nor ricotta. As @FuzzyChef mentioned in the comments, ricotta* is usually made with milk heated to 85C (185F), to which acid is then added to form curds. Mozzarella, on the other hand, uses a smaller amount of acid to enable stretching, then rennet at 30-32C (86-90F) to form curds. You cannot make mozzarella without rennet.

Your milk not coagulating might be caused by the raw milk, method, lack of acid/coagulant, or temperature. Since you brought it to the boil as well as added more vinegar, we can eliminate the last two. There might be something special about (your) raw milk that prevents it curdling (I have read that milk has some ability to buffer pH), or the jumbled method that you used (adding acid at low temperature then boiling with more acid) that prevented it from curdling, but I would expect at least something to happen.

*@rumtscho pointed out that "true" ricotta starts with whey, but most online recipes (e.g. this one) tell you to curdle milk with acid for ricotta, which is the cheese that I call ricotta in this answer.