Very often there are reports that an IPFire system won't come up any more after installing a Core Update. We acknowledge that we have bugs, but most often this is caused by hardware failure instead.
IPFire systems often run for many months or even years without being rebooted. If an update is then installed and the system is rebooted afterwards, huge parts of the hardware are briefly switched off and back on again. Harddisk controllers are re-initialised and alike. Sometimes this just fails.
Often harddisks won't spin up any more. Sometimes they do but lost parts of the data that was stored on them. In that case the only way is to replace the failed device, reinstall and restore the last backup.
This is one of the most common issues and often undetectable before. Most system data is kept in memory and read at boot time so that they system does not need to access it. When it boots up again and the essential programs cannot be read from disk any more, the boot fails. Also updates that are installed might not end up on disk although the disk reported a successful write operation.
If you are using a flash device you might be suffering from bad flash.
Sometimes network interfaces are just missing after a reboot because they fail to initialise when the system is booting up. Sometimes these can be replaced.