DIAGNOSIS This is usually a power-saving or IP address conflict issue. The Hub's Wi-Fi chip can get stuck in a low-power state, or your router might be giving it a new IP that causes a conflict with another device.
FIX First, in your router's admin settings, assign a static IP address (or DHCP reservation) to the Echo Hub. This stops IP conflicts. Then, on the Hub itself (via the screen or app), go to Settings > Network, forget your Wi-Fi network, and rejoin it. This establishes a fresh connection.
IF THAT DIDN'T WORK The problem could be your router's band steering. If you have a combined 2.4/5GHz network with a single name, the Hub (which is 2.4GHz only) can get confused. Log into your router and temporarily create a separate, dedicated 2.4GHz network with a different name (like "Home_2.4G") and connect the Hub to that. It's less convenient but far more stable.
HEADS UP Avoid mounting the Hub in a metal electrical box or directly on a thick masonry wall. These can severely weaken the Wi-Fi signal, causing intermittent drops that look like software issues.