I have been a Contacts+ user for quite a while - I found it very useful and the interface was convenient.
A few years ago I bought a Sony Xperia Z2, and after transferring my apps to this new phone, I immediately began to experience problems with regards to slow performance on the phone and screen freezes/lockups lasting 1-3 seconds.
I chalked this up to the Sony implementation of Android - so I rooted that phone and put Ressurection Remix (an open source android variant) on the device. All of the problems went away.
In December of 2015, I bought myself the newest Xperia, the Sony Xperia Z5. After transferring everything over (can you see where this is heading?) I, once again, experienced lag on the OS, stuttering screens, and freezes/lockups lasting 1-3 seconds.
This time I didn't just want to bail on the Sony OS (android version 5.1.1), especially since (a) I had this problem before and (b) no one else on the internet was reporting this issue. I downloaded a few apps to monitor CPU usage and internet usage... top of the charts? Contacts+
After deleting Contacts+, clearing the cache and rebooting...voila: zero lag, no stutter, and the screen is as smooth as butter.
It's important to note that I never had these issues on any of my Nexus devices with Contacts+. Conclusion: There is something about Contacts+ and the Sony implementation of Android that seriously hate each other....
...no more Contacts+ for me until they figure out the issue. The Xperia is too nice a phone to abandon, and the Sony implementation of Android is really quite nice.
Sorry guys....I'm bailing for a while...
I really think you guys need to get a hold of an xperia and check it out yourselves. It happens without fail on both the xperia z5 and the z2. (does not seem to happen on my xperia z3 tablet, however). There is some interaction with the Sony Android build that contacts+ is pretty Cranky about.