Temperature in the fermentation fridge had dropped drastically a couple of days ago, reaching -8.6 ℃ and causing the extremities of the fermenter contents to start forming ice. In hindsight This may be due to there only being a single, solid item in there, which takes a while to cool down and causes the air temperature in the fridge to get much colder than usual while keeping the average interior temperature warmer than usual. Then again, the thermostat is mounted inside the fridge and should be sensing the air, not the fermenter contents, so I don’t know what’s going on.
Either way, from now on I’m going to use the fridge on a low setting so that the difference between a newly added fermenter and the air inside the fridge is minimal. It’s all thawed out again now and no leaks have sprung, but I’ll have to inspect the threads and seals carefully when cleaning the vessel. On the bright side my brew appears to be clearing gradually, which is nice.
#wisdom: decrease the temperature slowly when cold-crashing to avoid freezing the brew. When using the Inkbird it may be worth placing the sensor inside a separate bottle of water to act as a thermal buffer.