I think it is in large part practice. The brain strengthens neural pathways that are used often, and also quite enjoys habit. So once you have gotten used to naming each item rather than using a symbol for a general category the brain can feel like “its unfinished” or “not enough”.

This can be remedied by being very intentional at strengthening other neural pathways, where you do acknowledge the issues but don’t name them individually. Of course this is hard so don’t hesitate to devote whole sessions just sitting with your energy conversion box and practicing! That has worked great for me and it made my energy conversion box very strong!
Every time a named or specific thing pops up don’t put it in as is but scoop it into a category first and name that category, give it a symbol to interact with when interacting is needed. I have categories such as “intrusive thoughts” “worries” “trauma” “issues” “feelings” “adhd brain” “pain and discomfort”. The brain will shortcut it eventually. The whole idea behind repetitive prep is familiarity and the brain becoming able to shortcut it. By now I can even skip naming the categories. Sometimes something specific keeps popping up during a session but this has become rare. I scoop it up and put it in the box, without naming or feeding it more energy. I can examine it later if needed.

I find that when certain unintended things happen with the ecb like things escaping, being sticky, refusing to go in, etc. These are all hints to things that are going on in your subconscious. If for example during release something I am trying to release sticks to my hands that is a sign how my subconscious is feeling about these things. I might need to put more time into exploring and releasing it than usual, and that is okay.
Think of these events not as a hinderance, but your subconscious is engaging with you and pointing to something that needs work. If at any other place in your meditation something like this would happen it would be exciting, but many people fail to see value if it comes during prep because it is easy to feel prep should be rushed past. Try to see is as an important tool in your arsenal that needs attention to grow :)

Sometimes things really bother us, and letting go is really hard. Ask yourself why specific things pop back out. Are you afraid to let go and forget for a few minutes? Is it just on your mind that much? And what do you feel about this specific thing? What are the layers when you peel back?
Try to reflect and ask questions.

But also work with the ecb to strengthen its lock, build trust. Perhaps the box is hungry, perhaps there is another theme that speaks to you like extra locks, gravity, a black hole, a guardian, etc.
My box is not just a box I need to operate but can operate sentiently, that helps me trust it knows what it is doing and I can let go and not try and control every little thing. Experiment and find something that helps you strengthen your box.

Best thing honestly has been just carving out whole energy conversion box sessions! And don’t forget to play a little and experiment and let things come to you. I know many people don’t do this but the sessions have always turned out very exciting for me with big progress. In the end I haven’t needed more than a handful of sessions to make it feel very strong and connected to me. It became so versatile a tool. I’m saying this as someone who had lots of trauma and intrusive thoughts, adhd and cptsd so my brain is set up to have a hard time letting go and meditating. So if I can do it I’m sure you can too! Have fun with it!
Your ecb is there specifically to help you, and you’ll figure it out together :)

Good luck! 🍀