I had the same issue before. Tried a lot of the internet remedies, but none really worked. Feel like it has to do more with how long you boil it and at what temperature. Sometimes I feel like going to ask 7-11 or family mart how they do it, but it seems like they just put it in their pot and let it boil/simmer all day. Their tea egg leaves usually peels pretty easily.
I think it’s more to do with the eggs. I use the same method every time, sometimes you get a carton of eggs that are a PITA to peel, most times have no issue.
'Really fresh eggs can be more difficult to peel when boiled compared to eggs that are a few days old. The reason for this is because fresh eggs have a lower pH level, which causes the egg white to adhere more tightly to the inner membrane of the shell. As eggs age, the pH level increases and the egg white shrinks slightly, which makes it easier to separate from the shell.
To make fresh eggs easier to peel, you can try adding a teaspoon of salt or a tablespoon of vinegar to the water when boiling them. This can help to raise the pH level of the egg whites and make them easier to separate from the shell. You can also try using a spoon to gently crack the shell of the boiled egg all around before peeling it, as this can help to loosen the shell from the egg white.’