I have also have 100% CPU usage problem with 3.1.2.
After doing some "git bisect", the problem seems caused by this commit: 9484dc1a468a1e5323abc0ea0666c353ba7678d6
The previous commit 75b58b16a546deb4bb7ca25ca7520ec8788ddf2a and before is fine,
after that all builds start with immediate 100% CPU usage.
And if the first pool is not stratum, 3.1.2 will hangs on start.