I think people are reporting that the whole router reboots rather than just the DSL connection dropping.
Including that any RAM-only logs are lost at reboot (if not flushed to flash before it happens).
For the latter I could understand downgrading the DSL version.
But that is only going to help with restarts if that is crashing the whole router.
If Zen do not know which program or hardware driver is causing the router to have unplanned reboots it should not be guessing with fixes for a different class of problem such as line instability or Wi-Fi settings.
They would probably need the router to be talking to a syslog server so that it has messages right up to the point of failure.
Typical problems that adding new features can cause would be out of memory while chipset firmware/drivers could either cause a kernel panic or system hang if not handled gracefully.
If it only happens when the system has been running for a certain amount of time it can be a memory leak or when a scheduled job kicks in.
For a system hang it may have a low level (hardware-based) watchdog that reboots the system if it becomes unresponsive - it's not uncommon for devices intended for continuous unattended operation.
prlzx on Zen: FTTC (VDSL) at ~40Mbps / 10Mbps
with IP4/6 (no v6? - not true Internet)