I have a fairly heavy e-bike and I'm a fairly heavy rider. My bike has mechanical disc brakes, and around 5 months ago I was having an issue where the brakes became useless, as in when I applied them they did nothing.

I think this was due to the extension of the brake cables so I tried to tighten them. After I did this when I pulled the brakes they seem to catch for a second then they would disengage with a click sound.

I ended up taking it to the bike shop who said they repaired by adjusting the brake cables. It was fine for a few months but again the problem seems to have occurred (though in this case it's just the front brake). I did try tightening the brake cable and it seems to have made it better (but I have yet to properly test this).

Why does this happen? I got the impression from the repair it was a pretty straight forward, anyone have any suggestion on how to fix this?