How to respond to chat (web widget) tickets via mobile app?

A client of ours (1 Agent only) is often on the road and thus, is forced to use the mobile apps almost 50%. 

However, the experience is extremely limited and we're considering to switch systems, as we encounter several problems: 

• he cannot answer Chat Tickets (via embedded web widget) in the Support App and needs to switch to the Chat App. Which is not really efficient, but can be dealt with. 
• however, he's neither able to reply to a client's request in the Support App nor in the Chat App, when the Ticket was generated, while he was offline. ("Offline Chat Ticket"). He gets the error: "Another agent is talking to this customer … " although, he's the only agent. This means, he cannot reply to the customer request until he's back at the store?! 

Is this a bug or has anyone solved this issue in another way or can recommend another solution? 

The customer service promised to take care of it — but nothing has changed over the course of a year. 

Thanks!