LineageOS: Phone and Contacts crash I've switched from Cyanogenmod to LineageOS using the experimental build and then flashing a nightly build afterwards. This worked great except for the fact that the phone and contacts app kept on crashing. I reflashed the nightly and -- to be sure -- this time I flashed the GApps immediately after as well. 

I've tried both the Gapps "stock" package and the "micro", because I thought the problem could lie within Hangouts. It didn't. 

When I boot my phone up, I get android.process.acore has stopped working (or something along the lines of that; I'm using the German translation) and this message get's repeated everytime I try to open the phone, messages or contacts. All other apps seem to work fine.

Interestingly enough, I can get called. The aforementioned error message is displayed, however, I can tap on Kill app without killing the conversation.
If you have the cynogenmod zip file somewhere stored then I think it is very easy to restore it. Just extract the cynogenmod on your computer and go to system->apps and copy the apks which are not working (eg.Phone, Contact in your case). Now also extract the nightly build which is giving you errors and go to system->apps and find the phone.apk and contacts.apk and delete it. Now just paste those apks which you had copied from CynogenMod and compress the modified Lineage OS in zip format. Now you are all done. Flash the newly created zip file and comment here if it worked (which is going to work in most case).