I had a similar issue after almost bricking (you wouldn't want to know...) and sd recovery - safe for the fact that after re-rooting with rupor's minimal the reader would freeze at the opening book screen time and again and only sd recovery was able to make it run again.
However, I did sd revovery and hard reset/factory reinitialization. Afterwards I still noticed that curiously some traces of the rooting procedure. Most notably the debug option would still pop up in the top bar whenever I connect my reader to my pc. So I did some sd recoveries and some hard resets and ran all the disable flashes. The traces disappeared, but rerooting still resulted in freezes.
In the end I rooted with boroda's minimal root, which worked as far as I can tell.