TeamViewer 6 Host not work

TeamViewer host was installed to the client a few years ago. Now all clients with "old" installations see a window with the inscription "not ready", the ID field contains " -". We previously used the purchased TeamViewer 6, but later switched to the subscription model. Everything worked fine for a while, and at a certain point in time, we stopped connecting to computers saved in groups. The only way to get back access to such a "dead" computer is to uninstall TV6 and install the current version (15). As a result, after buying a working product, we have to spend several minutes on each uninstall and installation of the application. Sometimes it requires a multi-kilometer trip "feet" and manual intervention. How to access previously installed TV Host V. 6? we are now being offered to renew our subscription, but the labor costs incurred by my employees over the past year are being stopped