[NiLuJe]

@Ruskie_it: That's a known side-effect of a couple of different things, and isn't limited to the PW2/FW5.6.

First, there's a race condition that might bork the Kindlet jailbreak. Granted, that one should lead to a failed startup no matter what, but I personally only very rarely experienced it at other times than a cold boot.
Second, there's a hard-limit on the amount of time allotted to a Kindlet to start-up.
Third, the Kindlet framework is lazy-loaded.
Fourth, depending on the device/amount of books/collections, the framework might be crunching numbers for a while after a cold boot (or a framework restart).
Five, a cold boot means cold caches, which exacerbates nearly all of the issues above.

All of this means that the first startup of KUAL has a greater likelihood to fail, especially if the framework is busy crunching numbers (bootup/indexing), which gets worse the more books/collections you have, or if the KUAL extensions folder is large/complex (takes more time to refresh the cache).

The second point can be alleviated by the use of the gawk extension, since that makes the parser faster, but it's by no means a silver bullet.

(And before someone asks, no, the bootstrapping process of KUAL is already slimmed down and deferred as much as reasonably possible to try to fit inside said window of time, so we can't really do better, we kinda have to parse the extensions at some point when the cache is cold to show something, and that's a mostly blocking process on a cold cache).