We are aware of the issue regarding the message input box disappearing from the docked chat. Another part of the chat is being worked on and this was an unintended side effect. However, the embedded version of the chat is still working fine, so please feel free to use that. You can use the search function in the Contacts tab of the embedded chat to look for online users and begin a chat.
The embedded chat is located at https://www.pixelmarket.net/customer/account/inbox/ or from within your account, as well as in your vendor panel for sellers.