What causes an idle game losing progress on long offline periods?

Offline gains are accumulated into a 32- or 64-bit number that overflows when elapsed time and multipliers grow large, wrapping the total to a wrong or negative value.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix an Idle Game Losing Progress on Long Offline Periods in Unity

Quick answer: Use a big-number representation (mantissa plus exponent) for resources and compute offline gains with that type instead of fixed-width integers.

When a player returns after a week and their currency reads zero or negative, your accumulator overflowed. Big-number math fixes idle accumulation. Here is how.

How to fix it

1. Adopt a big-number type

Represent large resources as a mantissa and exponent (or use a BigDouble-style library) so values can exceed what long or double hold without overflowing.

2. Compute offline gains in that type

Multiply rate by elapsed seconds using the big-number type, and clamp elapsed time to a sane cap if you award offline progress, so the math never wraps.

3. Persist and format consistently

Save and load resources as the big-number type and format them with suffixes (K, M, B, aa) for display, keeping internal precision separate from the shown value.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unity error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

A crash you can name from its stack trace is a crash you can usually fix in minutes.