Machine Does Not Automatically Switch Between Telephone and Fax

Troubleshoot by checking the items below.
Is the RX Mode Set Appropriately?
Check that the RX Mode is set according to your fax purpose, and change the setting, as needed. Changing Fax RX Mode and Setting the Action when Receiving a Fax
When a regular telephone is connected, set the RX Mode to [Fax/Tel (Auto Switch)].
Is the Ring Start Time Too Short When the RX Mode Is Set to [Fax/Tel (Auto Switch)]?
If the time until ringing starts after receiving a fax is too short, the machine may not be able to determine that it is a fax and you may hear an incoming ring when the fax is received. Check the [Ring Start Time] setting, and increase the time, as needed.
[Home] screen on the operation panel [Fax] [RX Mode] [Fax/Tel (Auto Switch)] [Ring Start Time] enter a time [Apply]
Is the Line Status of the Sender Good?
If the line status of the sender is poor, the machine may not switch to fax at a fast communication start speed. Check the [RX Start Speed] setting, and decrease the speed, as needed.
Log in to Remote UI in System Manager Mode [Settings/Registration] [RX/Forwarding Settings] [Fax RX Settings] [Edit] in [Basic Settings] in [RX Start Speed], select the speed [OK]
On the operation panel, select [Menu] in the [Home] screen, and then select [Function Settings] to configure the settings. [RX Start Speed]
Does the Machine Have Sufficient Free Memory?
Check the faxes received in the memory of the machine, and print or forward them as needed, and delete any unnecessary faxes. Viewing and Printing Faxes Saved in the Memory
Does the Sender's Fax Machine Support a Fax Identification Signal (CNG Signal)*1?
If it does not support this signal, the machine will not switch automatically to fax receiving mode. Change the RX Mode to [Manual] to receive faxes manually. Changing Fax RX Mode and Setting the Action when Receiving a Fax
*1 The fax identification signal (CNG signal) is a beeping sound transmitted by the sending fax machine.