Suddenly, incoming callers do not hear a ringtone on their end anymore. Nevertheless, calls can be completed without further issues - just the calling party has the impression that nothing happes during the silence until we do pick up. Generally, my setup is working for years without such issues.
The setting is: Dual SOHO with two freepbx installations in two different settings. Each on deidicated supermicro servers behind a pfSense firewall. No changes on other hardware or software in the relevant timeframe. No obvious causes of NAT issues that did not exist before. Each FreePBX 13, on based on the distro on Centos 6 and one installed on Centos 7. Same effect on both.
I did sense that one update (at least of module framework) did take unusually long and had to be initiated again. On the two installations mentioned plus my two warm spares on virtual machines.
If I recall correctly, there was one way to reinstall all modules command line while keeping the configuration. Unfortunately, I could not find how to do that. Can someone please remind me?
Next step, I would be glad to report if that helps and/or follow other advice.