For the most part, FreeBSD on a Raspberry Pi is about
as reliable as any OS can get. I've used a quartet of 
Pi2 machines running -stable for several years now as
name, mail and web servers. One key requirement is to
use fast, new microSD cards that are much larger than 
seem necessary. In some sense the microSD card is 
treated as a "write once" device. The moment it starts
garbage collection the write speed will fall to the
point of causing intermittent trouble. 

There are, however a few little niggles that come up.
The Pi was never intended as a "production" server. In
particular, the connectors and power supplies are frail
by industrial standards. I've had several supplies fail,
in a few cases connectors have required re-seating and
in one case a micro-USB connector on the Pi's motherboard
broke and had to be bypassed.

The Pi draws considerably more current on boot than when
up and running. It's not unusual for a machine to run for
months, then fail to reboot after shutdown if the power
supply or its connector has deteriorated meanwhile. It's
inconvenient to get at, but the +5 volt and ground pins
on the GPIO header are a good place to check. It's important
to watch voltage during boot, not later on. Many DVMs
can't read fast enough to show a voltage sag that causes
a reset. If the machine reboots while it's booting, the
power is a prime suspect. 

While the Pi does have a "voltage monitor" accessible 
using sysctl -a, it's a go/no-go test at 4.65 volt.
Above 4.65 it simply reports 5 volts exactly. Dunno
what it says at less than 4.65, if it'll even boot.
In RaspiOS, that's what triggers the undervoltage
lightning bolt warning.  

Out-of-the-blue network problems have been very rare.
It never hurts to re-seat connectors, but so far all
of my network failures have been self-inflicted, usually
by getting cables or hosts mixed up.

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