Your comments

Of course you have helped me ...

Thank you very much for all the explanations.

The version of the system is not the problem, with the previous versions and the same problem, I reboot the NAS and the Java application works again, it has to disappear, and it is not good to restart or apply Java.

My current version is, the last one, I am the last one to have it updated, in the same way that the new tares / problems, other old ones disappear, is the never ending of the operating systems.

Maybe RAM, I only have 4Gb, but with QNAP, who risks spending more money? I have bad experiences about it, and I'm not the only one.

According to the QNAP itself, my TS-653A has an Intel® Celeron® N3150 / N3160 1.6 GHz quad-core processor.

And I use the QJDK8 package provided by QNAP Club

WOW !!!  Too many books to convert, impossible.

Anyway, I think there is a problem in my QNAP and Java programs, while they are working, they stop doing it and the only way to get them back to work is to restart the system, and that can not be the case.

Please, make readable online MOBI & FB2 files, :D