We updated the prometheus library in 3.4. It looks like the new update does not allow metric name starting with number and thus "10g" is causing it to panic (i am assuming you have a temperature controller with name 10g). For the time being changing it to something else that does not starts with a number might fix it (e,g. TenG or IOg) or just disable prometheus from the preferences. Meanwhile I'll check if we can prevent this in reef-pi side , i.e check if the metric name is valid or not, and error instead of panic if its invalid.
This is not a nice bug, it basically locks you out and you have to pitch the database and start over. It appears that not only the temp definitions need to not start with a number but it also applies to the lighting. I was just about done and have to start over once again. I could just turn Prometheus off but rather like having the data.
Oh well tenth time is the charm...wait maybe i have that wrong