I had the same problem and I found a solution, but maybe is not the same 'problem source' as yours.
On my case, I had more than 24000 contacts as showed by gmail[dot]com on desktop browser, a single contact gets auto-duplicated 24000 times!
I needed to remove then from the web and then re-sync again my Nexus 5 to get it working fine again.
Detailed explanation took from my post at Google Groups (title "Contact List and Contact Detail most times Blank after 4.4.4 update"):
From Contacts at gmail[dot]com on desktop I could use the tool 'Find and merge duplicates' under the 'More' menu (labels can be a bit different, I'm translating from the Spanish texts). I needed to use it several times to get all duplicates removed, since the tool has some internal limit per task.
Thats was easy, but my phone didn't get in sync, contacts synchronization spent a lot of time to do the task and never finished. I did some failed attempts as: I went to Android Settings -> Apps
, selected the 'contacts sync' app and deleted cache and data; I tried the same for the contacts app and dialer app (anyone looking to do this same be careful with any local data not synced since you will lost it; do a backup first if you will attempt but this was not the solution on my case).
Finally, the key was to unlink my gmail account from the device and linking it again, from Settings->Accounts->Google account->Synchronization->top right menu->delete account.
I tried to do the same with the Gmail app as for previous apps
, removing the data from settings->Apps
->Gmail before linking it again, but not sure if this was needed. Once it finished loading again my emails, contacts, calendar events, and all other things (it take a bit, but was fast, you can review progress on Settings->Accounts->Google account->synchronization), my phone started to be faster but not enough still (a bit slow opening contacts but worked). I restarted the phone to ensure any 'garbage' in memory doesn't affect performance, and it runs fast now.
Hope it helps someone,