Invite the person who has been quiet without asking them to explain their absence first.

A gap in contact builds its own barrier. The longer someone has been out of touch, the more they assume a return requires an account of where they went, and the account is often the exact thing they cannot face. Illness, money trouble, depression, shame about the silence itself: any of these makes the explanation harder than the absence. So they stay away, and everyone reads it as choice.

Send the invitation with no preamble and no questions attached. Mention a specific day and make it easy to decline without a reason. If they come, talk about anything other than why they were gone.