race condition

When two events/threads/promises (or some heterogeneous matching of two of these) act at the same time and users experience different results when A starts or finishes before B and the discrepancy is undesirable (id est, it should not matter whether A or B "wins") then one has a bug that could be called a race condition, to wit, a condition in which there is a race for the right actor to succeed first. Boo hoo.