Have the A4 model.
Also having the constant reboots.
What i did try:
- 1.32NA firmware. Same issues.
- 1.32NAB09, beta firmware.Same issue. Cannot revert back to previous firmware but that will solve in time.
Opened the cover some days ago. Noticed the ceramic heat sinks are quite hot.
So today i found an obsolete CPU cooler. Disconnected the fan from the CPU heat sink and put it onto the open DIR-655.
Put it running on 5Volts otherwise the fan is freezing the DIR-655

with a separate power adapter (fill fix this later...)
Until now and this is a record for this DIR-655: almost 6 hours up and running without any reboots.
So i think it is a heat issue in the A4 models.
So anybody with frequent reboots varying from minutes to hours: try getting it cooler.
Will try to find some traditional heat sinks and glue them to the chip-set and see if it runs without the fan this way. If not will mount the fan fixed into the top of the DIR-655.
A small 70x70 fan costs about 7 Euro so that will not kill you. If you need it to run on 5 Volt get an 7805 with it to reduce the input voltage and you can directly tap it from the plug !