If non of the workarounds help (meaning you get random reboots even after reinstalling the latest OS version, performing a hard reset, cleaning the phones insides and taking out all cards) then you have a hardware issue and should contact support to get a replacement. Either call them or use the request form and post your request number here to speed up the process.
While a forum where people come who have problems with a product can make it seem like a issue is very common, 280 people are a low number compared to the thousands who bought the FP2.
If this was a bug, then a majority of users would have this issue and Fairphone would have probably at least found the root cause yet. So far nothing indicates that this is a bug.