Why do some bugs happen only sometimes?

Because they depend on non-deterministic conditions that vary between runs, not because they're truly random. A race condition depends on which operation finishes first; a timing-dependent bug needs a specific window that's only sometimes hit; a state-dependent bug relies on memory that varies. The bug has a real cause, but the trigger is inconsistent, so the bug appears and disappears. Flaky doesn't mean random, it means the triggering condition is non-deterministic, which is why these bugs are hard to reproduce but still have an identifiable root.

How do I fix a flaky bug?

Identify the non-determinism behind it. Capture and group occurrences to reveal what they share despite the inconsistency, a concurrency pattern, a timing window, a particular state, which points at the source. Then address the root cause: fix the race condition (with proper synchronization), remove the timing dependency, initialize state properly, or control the randomness. Treating a flaky bug as having a real (if non-deterministic) cause, rather than as random, is what lets you find and fix the source of the inconsistency.

What Causes Flaky Bugs?

Quick answer: Flaky bugs, ones that happen inconsistently, are caused by non-determinism: race conditions, timing dependencies, uninitialized state, randomness, and environmental factors. They depend on subtle conditions that vary between runs.

Flaky bugs, which appear and disappear unpredictably, are among the most frustrating to debug because they won't happen on command. They have specific non-deterministic causes. Here's what causes flaky bugs.

Why Bugs Are Flaky

A flaky bug happens sometimes but not others under seemingly the same conditions, which means it depends on something that varies between runs, a source of non-determinism.

Race conditions, the bug depending on which of two concurrent operations finishes first, which varies
Timing dependencies, the bug needing specific timing that's only sometimes hit
Uninitialized state, behavior depending on leftover or uninitialized memory that varies
Randomness, the bug triggered by certain random values that don't always come up
Environmental factors, load, timing, or external conditions that vary between runs
Order dependencies, behavior depending on the order operations happen, which isn't fixed

The common thread is non-determinism: the bug depends on a condition (timing, concurrency, randomness, state) that isn't the same every time, so it appears flaky.

Why Flaky Doesn't Mean Random

Flaky bugs feel random, but they're not, they depend on real conditions that simply vary. The flakiness comes from the trigger being non-deterministic (timing, concurrency), not from the absence of a cause. This is why they're hard to reproduce but still have an identifiable root.

Bugnet captures crashes and reports with context and breadcrumbs, so flaky bugs that crash surface with the conditions around them. Capturing many occurrences of a flaky bug can reveal the subtle condition behind the inconsistency.

Finding the Cause of Flaky Bugs

Finding a flaky bug's cause means identifying the non-determinism behind it. Capturing and grouping occurrences can reveal what they share despite the inconsistency, a concurrency pattern, a timing window, a state. Then you address the root: fix the race condition, remove the timing dependency, initialize state, or control randomness.

Bugnet groups occurrences and surfaces shared context, helping reveal the condition behind a flaky bug. So flaky bugs are caused by non-determinism, race conditions, timing, uninitialized state, randomness, and finding them means identifying and fixing the source of inconsistency, not treating them as random.

Flaky bugs are caused by non-determinism, race conditions, timing, uninitialized state, randomness, that varies between runs. They're not random; capture and group occurrences to find the subtle condition, then fix the source of inconsistency.