Every device on a network makes its own decisions about which radio band to use, how hard to hold on to a weak signal, and when to give up and reconnect. Two devices sitting side by side can therefore behave completely differently, and that is the single most useful clue when only one of them keeps dropping.
Older or cheaper wireless adapters are less tolerant of interference. They hold on to a marginal signal longer, fail, and then reconnect from scratch, which is why the drop feels sudden rather than gradual. Newer devices tend to switch bands quietly before the connection collapses.
Power saving is the other common culprit. Laptops and phones will dim the radio to save battery, and some do it aggressively enough that a connection idles out. The device looks connected, but the first request after a pause takes several seconds while the link wakes up.
Finally, networks with an extender or mesh can leave a device clinging to the wrong access point. The device stays attached to the unit it first joined even after you walk to the far side of the house, so the signal quietly degrades until it fails.