Your meetings and chats are in Networking: chats in the list under Chats, pending requests under Meeting requests, and accepted meetings also in My Schedule. If something is missing, check these causes in order.
You are signed in to a different account
Check that you are signed in with the email address you used to join the event.
Open Account > Troubleshoot. The Account check shows the email you are signed in with.
If it is not the email you registered with, select Not you? Sign out and sign in with the other email.
If you joined the event in the other app, open the event there.
Deleting the extra account is permanent and also removes its event data. If you can't tell which email you used, ask the organizer.
Networking is off for your ticket
When networking is off for your ticket or attendance type, the Networking tab is hidden and the app shows Networking settings changed: "Networking has been disabled for your ticket or attendance type. If this is an error please contact the event organizers." Contact the organizer.
You skipped networking when you joined
Networking then shows "Don't miss a chance to build new connections." with a Start networking button instead of your chats. Select Start networking and complete your event profile. You can also open Account > Start join process again.
You have not finished joining the event
A sheet with "Complete onboarding to get started" and Finish onboarding covers the tabs until you complete the join steps. Account > Troubleshoot > Event access shows "Joining not finished". Finish the steps; the Networking tab appears after that.
The chat is hidden
A chat you hid with Hide & Mute leaves the main list and stops sending push notifications.
Open Networking and select the Hidden filter.
Press and hold the chat (mobile app) or right-click it (web app, wide window).
Select Unhide & Unmute. The app shows "Chat unhidden".
You blocked the person
Blocking a person hides your chats with them and stops their messages and meeting notifications.
Open Account > Blocked users.
Select the trash icon next to the person. The chats come back.
The list has not loaded
With no connection, chats show "You seem to be offline" above the message box. Reconnect, then pull down on the Networking screen to refresh. If the list stays empty, open Account > App cache and select Clear app cache.