Similarly, I spent 6 weeks on a kernel token-ring driver intermittent initialization issue. This required kernel restarts over and over to observe the issue. Breakpoints were useless as they hid the issue. Turns out initialization in a specific step was not synchronous and reading the status was a race condition. It tooks weeks of staring, joking around, thinking, bs'ing, then suddenly, voila. Changed the order of the code, worked.