This could be a number of things, some of which you can control.
For example, you cannot control
Whether the receiving fax / server generally stays connected or hangs up suddenly
The condition of the phone line - voice transmission will still work when data transmission struggles.
Phone Line Condition
If the issue is the individual phone line in just that part of the house / office, you might have better results from a different phone connection. If the issue is the condition outside of your house - for example, old or squirrel eaten wires, you cannot control this - and the phone company might not care since the phone lines need only work for voice transmission to meet "spec". (You could certainly ask your phone provider - laws / policies may be different where you are located.)
Reference and Resources – (More) Places to find help, solve problems, and learn how to use your Printer
Printer Homepage – “Things that are your printer”
NOTE: Content depends on device type and Operating System
Categories: Alerts, Access to the Print and Scan Doctor (Windows), Warranty Check, HP Drivers / Software / Firmware Updates, How-to Videos, Bulletins/Notices, Lots of How-to Documents, Troubleshooting, User Guides / Manuals, Product Information (Specifications), more
When the website support page opens, Select (as available) a Category > Topic > Subtopic