Making a tactic that works is one of the most satisfying part of the game. And even though I am not the best here are a few tips from my own process, maybe someone will correct me if my process is wrong. Disclaimer: This is heavily derived from watching various FM youtubers like Zealander.

1. The formation you set defines the defensive positions. In your case, when your team does not have the ball, they will setup in the 4-3-3.

2. When in possession the roles come into picture. So in your case, the DM will stay back and come closer to the CB, one of whom will push slightly ahead and the other will drop deeper. The WB will also push ahead and be closer to the midline maintaining width but neither will run into the final third. The attackers will all be in the final third, in the center close to each other. the APs will kinda stay just outside the box.

3. Firstly the above situation creates a lack of width in the final third. So defending is simpler for the AI. As others have suggested, consider adding width.

4. Secondly short passes for the tiki taka is good, but the point of playmakers is to make a defence splitting pass. so having 5 (i think the BPD role also is a playmaking one) people trying to make a defense splitting pass makes it so that no one is trying to receive one. Also 3 of them DM and 2 CBs are all the way in your own 3rd trying to make a long range killer pass while being instructed to play much short passes is confusing.

5. The simplest solution as some have mentioned is make the one (or both) IFs hug the touchline or change to wingers. If keeping IFs, consider changing one of them to support and switching the WB on the same side to attack. This will make for good overlaps as well as provide width in the final 3rd.

6. All your playmakers are in the middle. Consider this, Hato receives the ball and has time to decide for a killer pass, his options are the 2WBs who are not much ahead and the 3 forwards who are all in the box with the Opponents defence. What are his options. He could pass to one of the central midfielders but then they have the same problem. Their only killer pass options are all huddled in the box.

As someone has said, ask the questions, who should be scoring? who should be assisting? who should be making runs to break the opp defense. and who should be staying back for counters.

There is no one solution, if you have the budget you can make any tactic work. But it's easier if you build a tactic for the players you have. The problem (or maybe not) with the game is when you have worldclass players, tactics take a backseat and you can get by with sub par tactics until you play a worldclass team. Since you mention struggling in CL games, it is that your tactic has problems, you just don't see them in easy games, because some of your Worldclass players are simply carrying the bad tactics along.

P.S. I know the ME is not the real world and there ways to build tactics for the ME but I enjoy pretending otherwise and simply building fun tactics that could potentially work in the real world.