There is a colleague on many teams who used to come to lunch and now does not.
There is a colleague who keeps choosing the desk by the window, and quietly negotiates whichever seat puts them closest to the wall in meetings.
There is a colleague who declines the pub most weeks, and people have stopped asking.
For some of those people, the explanation is misophonia.
Misophonia is a neurological response to specific repetitive sounds. Chewing. Tapping. Sniffing. Pen clicking. Throat clearing. The brain's response is involuntary, immediate, and disproportionate. Not annoyance. Closer to a panic response.
Most adults with misophonia have built their working life around avoiding triggers, without ever naming what is happening. They eat at their desk. They take walks at lunchtime. They wear earbuds for “focus” that are actually for protection.
What it costs them is rarely the work. It is the social architecture of work. The casual chat over food. The team lunch where relationships are built. The promotion conversations that happen at the bar.
Read as antisocial. Actually neurological.
If someone on your team has stopped coming to things, please ask once, kindly, in private, what would help. The answer might be simpler than either of you expect.