Almost every custom ROMs are not stable. There are some bugs in it. Some have issues with alarm or VPN or data connectivity or wifi etc. It will be written in the download page from were you have downloaded it. The stock ROM is the stable form of android. But the only disadvantage of stock ROM is it's boring and not as customized as a custom ROM. There is only one method to fix this issue. You will have to flash another stable ROM like cyanogenmod's stable ROM or any other stable ROMs. Hope I helped.