"Sometimes doesn't arm" that's usually mag if you waited long enough for the GPS to be green. I find that if it is sitting on the ground, the mag is less likely to be green. INS13 only inits (init is required for arming like gyro init with Basic is required for arming) when both GPS and mag are green at the same time, after that they can go back to orange but INS13 stays inited so you can arm. If the mag is the issue, then picking it up and doing a 360 pirouette with your body will usually let it go green long enough to init.
INS13 doesn't do the fast blink when it inits, but there is a change in the status LEDs when it inits. Watching the orange and blue FC LEDs blink you will see a slow orange, blink slow blue blink, repeat if there is an issue. After the 360 you may see that it is now slow blue, quick orange, repeat, and that it can be armed.
The easiest way to troubleshoot is with telemetry and a GCS laptop. Look at System Health.
WaitUntilTheBoardIsSteady and BoardSteadyMaxVariance are for Basic (not INS13) because only Basic calibrates the gyros. You are using INS13, correct?