Usually this is one of three things.
Permissions. If you're agency staff, you may be scoped to particular areas: payments and messages are commonly limited. Your admin can widen it.
Which account you're in. If you have more than one role, or work with more than one agency, check you're in the right one. There's an account switcher.
It genuinely isn't there. An archived act stops appearing in pickers. A cancelled gig moves out of upcoming. An offer that was filled by someone else is withdrawn.
If none of those explain it, contact us and say what you expected to see and where. Things don't vanish on their own, and if one has, we want to know.