LMR62421 Boost converter short circuit issues
First off, you probably want a schottky diode rather than a standard diode. Sounds silly, but that can make a massive difference I have found. Secondly, with all these types of boost converters, PCB payout is absolutely key. You probably want your input and output capacitors much closer to the chip. You can also try sticking a load on it, as some of these require a minimum load to startup (on the first page of the datasheet it shows that the efficiency is poor under light loads). 

The next thing to do is figure out how much current you are expected to pull from that thing and ensure your components can take it. If it is estimated to be a large current (this thing says it can do up to 2.1A) then you might want to make sure you have enough ground. You just have a small track, and most of these chips need a nice amount of ground plane to dissipate heat in order to work correctly. 

How did you come up with 10uH as your inductor value by the way? Another thing about the inductor, the datasheet mentions that ferrite based inductors are preferred, due to perating frequency. Did you ensure to go along with that? And your capacitors, with these types of chips, you want capacitors with low ESR (equivalent series resistance).

I think this issue may be simply down to the PCB design aswell as component selection. It has happened to me before. Hope this helps.