Lins2SD app error: could not load library libsigchain.so. What does it mean?
It basically means that some binary code cannot be executed on your phone. It appears the Link2SD app you use comes with a piece of 32bit software, but your phone is 64bit so it cannot execute the code.

LD_PRELOAD is a system variable which basically tells Android what code libraries should be loaded/executed when starting any process or app. It appears libsigchain.so was added to this variable, possibly by the Link2SD app itself. When the app tries to execute the system program /system/bin/sh, it tries to load the libsigchain.so file but fails, apparently because libsigchain.so is 32bit.

Another possible cause is that /system/bin/sh is 64bit but ligsigchain.so is 32bit. Because 32bit and 64bit software operate in a different way, the two can not be combined and the /system/bin/sh process cannot start and produces an error.

Either way, not being able to execute sh is a mayor problem for most apps working with root permissions as sh is used to execute scripts on your device. If you see such an error in other root-apps as well, this might be a problem with your Android ROM.

The solution to this might be either a software update from Lenovo or from a new version of the app. Try reporting the issue to the app developer, maybe he/she can give you the exact details.