Power bank turns off spontaneously
You have a couple of options, depending on how much you want to dive into electronics.


Find/buy a new powerbank that does not auto-shutoff
Find the current-sense resistor on the internal circuitry of your existing powerbank and change it out so that the device always thinks there is current flowing, or is more sensitive to your low-draw attachment. I was able to find a few websites describing this for specific powerbanks by searching.
Add a dummy load in parallel with your circuit, which wastes power, but does trick the powerbank into staying on.


It's also worth noting on the side, that you very likely do not have 50,000 mAh capacity in this powerbank, as others have noted. However, you ought to be able to get 16h of runtime with even a lower-rated powerbank if your claim of 60mA current draw is true.