If you’re using a MacBook, MacBook Pro, or iMac and tend to leave it running for weeks without restarting, you may have noticed a familiar pattern: the system starts to feel sluggish, CPU usage creeps up, and certain apps begin behaving strangely. A newly identified macOS networking bug may explain why this happens so consistently—and why a simple restart often “magically” fixes it.
The issue acts like a hidden countdown timer. After a Mac has been powered on for exactly 49 days, 17 hours, 2 minutes, and 47.296 seconds, macOS can stop terminating some network connections correctly. At first, the impact is subtle: the computer continues running, but it starts accumulating network connections that should have been closed. Over time, that buildup can balloon into hundreds or even thousands of unnecessary connections being managed in the background.
That’s where performance problems can start. Handling all of those lingering connections can drive up CPU utilization, contributing to slowdowns that feel like general system “aging.” Eventually, the situation can get worse once the system runs out of available network ports—commonly around 16,384. When those ports are exhausted, the Mac may be unable to open new connections at all.
At that point, many apps don’t work properly anymore, especially those that depend on creating fresh network sessions. What makes this bug confusing is that not everything breaks in an obvious way. Network connections that were already established may keep functioning normally, and basic connectivity checks can still look fine. For example, macOS may still respond to ping even though some apps can’t load data or connect the way they should.
Restarting the Mac resets the clock and clears the problem—until the same uptime threshold is reached again. In other words, the reboot doesn’t “repair” the bug so much as it restarts the timer.
The oddly specific 49-day limit isn’t random. The behavior appears tied to how macOS tracks the timing and duration of network connections using a 32-bit counter. A 32-bit value maxes out at 2³², which corresponds to 4,294,967,295 nanoseconds—exactly 49 days, 17 hours, 2 minutes, and 47.296 seconds. Once that maximum is exceeded, the counter overflows, which can cause the timing logic to fail.
This kind of time-and-counter overflow problem has shown up in computing before. Classic examples include older Windows versions that could become unstable after roughly 49.7 days of continuous operation. And a similar 32-bit timekeeping limitation underlies the well-known “2038 problem,” where systems that store seconds since January 1, 1970 in a 32-bit format can run into errors on January 19, 2038.
What this means for everyday Mac users is fairly straightforward: if you keep your Mac running continuously for long stretches—especially as a workstation, media server, or always-on laptop—you may want to restart it periodically to avoid performance issues and unexpected app/network problems. If your Mac has been up for weeks and starts slowing down or internet-reliant apps act unreliable, a restart may be more than a generic troubleshooting step—it may be the most direct workaround for this specific macOS uptime-related networking bug.
