Only users admitted by host can join the meeting room from waiting room

assuming you logged into your account at zoom.us clicked settings along the left side and then under waiting room settings you checked "all participants" go into the waiting room. if you did this on your account then I can only think that possibly the meeting was made by another account host. I have had users in my zoom account think that if they enable waiting room for all participants that it would apply to all meetings they attend or that they were made alternative host in. attached a screenshot but this is a setting for your hosted meetings only. 

There are options that can be set so certain people can bypass the waiting room:

Who should go into the waiting room?

• Everyone: All participants joining your meeting will be admitted to the Waiting Room. 
• Users not in your account: Only participants who are not on your Zoom account or are not signed in will be admitted to the Waiting Room. If not signed in, they will have an option to sign in. 
• Users who are not in your account and not part of the allowed list: Users who are on your account or signed in to a Zoom account at the domains you list will bypass the Waiting Room. After selecting this option, enter the domains, separating multiple domains by a comma.
• Users invited during the meeting by the host or co-hosts will bypass the waiting room: Users that the host or co-host invited during the meeting will by pass the Waiting Room. This applies to users invited directly through Zoom during a meeting or users invited by phone.
  Note: This setting doesn't apply to inviting a Zoom Room or room system. The invited room will always be placed in the Waiting Room. Live assistants who join meetings via the dashboard or administrators using a web-based controller are also exempt from these settings. 
• Allow participants in the waiting room to reply to host and co-hosts: Allow participants to chat back-and-forth with participants in the Waiting Room. Waiting Room messages can be sent to all participants in the Waiting Room or just individual participants. Only the host/co-host can see responses from those in the Waiting Room. This feature requires client version 5.8.0 or higher and is disabled by default. If enabled, the host and all participants will be required to upgrade to join meetings.

Source:  Waiting Room – Zoom Support