Regularly, every other day or so, I need to cold reboot my headless DietPi because it has stopped responding to ping.
I use it very lightly and infrequently for Jackett, VNC, and I also have the Discord webapp set as my Firefox homepage, autorefreshing and random intervals between 2 and 4 hours. Before setting up the webapp and learning a regular Discord install was not possible I did try installing Discord via flatpak and some other options, so there may be some extra bloat on my system.
Can you please tell if there is a log file that I can check after the next time I have to cold reboot, or even if there is one I can check now? I cold rebooted within the last two hours.
it depends on the effort needed to perform a new installation. If this is something that could be done quickly, why not. Probably you have a spare SD card. This way you could keep the original system. Just in case …