Likewise I have a problem with crimping fork terminals, (or spade, etc) and I don't trust any of the crimpers I have tried, I always give the wire a good pull, and invariably some, in fact, most, come loose.

So I now remove the insulating coloured plastic with pliers and crimp just the one half of the round metal with small cutter pliers in two places (with just enough pressure to crimp - otherwise you would cut the metal!) and then with small flat pliers I press and fold the other half of the metal over the first half. Difficult to explain, I know. After doing that, I slide the insulating plastic back in position.

Anyway, after discarding dozens of crimps done with the crimping tool, I now prefer to do it by hand, 100 per cent success and secure and it doesn't take long.