Updating from cm12 nightlies to cm12.1 nightlies worked but there was a problem with Google Play Services.

Flash cm-12.1-20150420-NIGHTLY-mako.zip and gapps-5.1-2015-04-19-17-13-22.zip as recommended here:

After booting some things don’t work, including GMail, throwing errors about Google Play Services.

The following worked:

$ adb root
$ adb shell
root@mako:/ # mount -o remount,rw /system
root@mako:/ # rm /system/priv-app/PrebuiltGmsCore/PrebuiltGmsCore.apk
root@mako:/ # mount -o remount,ro /system

Get new play services apk from:

$ adb install com.google.android.gms-7.3.28_(1863718-446)-7328446-minAPI21.apk

(Note: this doesn’t install a new PrebuiltGmsCore.apk in the location above. But now everything works.)