We've had a 4th gen time capsule for a few years and it never had any problems. We recently started using the guest network feature and it now frequently locks up. The green light will be on but it will be unreachable from the Airport Utility (from wired or wireless connections). I've been working from home and notice that this usually happens when the guest starts using it. So it will be working fine then lock up as soon as a device tries to log into the guest network. It doesn't do this every time, though. If I unplug to restart it then it works fine until a day or two later when it locks up again. My first theory is maybe the guest network is causing the TC to overheat, which would explain why it doesn't happen all the time. I raised the TC on a couple pencils so air could flow under it but the problem persists. The devices that have locked it up have ranged from iphones to Macbook Pros to a new Macbook. Another thought I had was maybe 802.11 AC devices cause the lockup. But I don't really know. Any other ideas besides getting a new one (or just going back to not using the guest network)?