How about the word 'contingency'. Here's the second of two senses listed on Merriam-Webster's online dictionary:
a.) An event (as an emergency) that may, but is not certain to occur
b.) Something liable to happen as an adjunct to or a result of something else
To be honest, I'm not familiar with sub-sense 'b', and while M-W seems to specify possible (but not certain) emergencies, I've found myself using 'contingency' to refer to minor hiccups and set-backs.
Also, note that 'contingency' also refers to provisions made to address such (possible but not certain) events. Strangely, that sense is not mentioned on M-W, but is listed in the Oxford Dictionary (10th edition; page 307).